Add SIMD impl of memset for LoongArch

[heiher]

Benchmark results on LA664:

• LASX

simd/memset<u32>/8      time:   [2.5735 ns 2.6308 ns 2.6957 ns]
                        thrpt:  [2.7639 GiB/s 2.8321 GiB/s 2.8951 GiB/s]
                 change:
                        time:   [−14.812% −11.240% −7.7107%] (p = 0.00 < 0.05)
                        thrpt:  [+8.3549% +12.664% +17.387%]
                        Performance has improved.

simd/memset<u32>/136    time:   [8.0049 ns 8.0098 ns 8.0159 ns]
                        thrpt:  [15.801 GiB/s 15.813 GiB/s 15.823 GiB/s]
                 change:
                        time:   [−51.251% −51.202% −51.145%] (p = 0.00 < 0.05)
                        thrpt:  [+104.69% +104.92% +105.13%]
                        Performance has improved.

simd/memset<u32>/1024   time:   [12.407 ns 12.414 ns 12.422 ns]
                        thrpt:  [76.770 GiB/s 76.824 GiB/s 76.866 GiB/s]
                 change:
                        time:   [−88.281% −88.262% −88.249%] (p = 0.00 < 0.05)
                        thrpt:  [+750.97% +751.94% +753.34%]
                        Performance has improved.

simd/memset<u32>/131072 time:   [2.4655 µs 2.4668 µs 2.4685 µs]
                        thrpt:  [49.450 GiB/s 49.485 GiB/s 49.512 GiB/s]
                 change:
                        time:   [−81.223% −81.209% −81.195%] (p = 0.00 < 0.05)
                        thrpt:  [+431.76% +432.17% +432.57%]
                        Performance has improved.

simd/memset<u32>/134217728
                        time:   [4.4058 ms 4.4173 m`s 4.4313 ms]
                        thrpt:  [28.208 GiB/s 28.298 GiB/s 28.372 GiB/s]
                 change:
                        time:   [−67.246% −67.154% −67.062%] (p = 0.00 < 0.05)
                        thrpt:  [+203.60% +204.45% +205.30%]
                        Performance has improved.

simd/memset<u8>/8       time:   [3.2015 ns 3.2029 ns 3.2050 ns]
                        thrpt:  [2.3247 GiB/s 2.3262 GiB/s 2.3272 GiB/s]
                 change:
                        time:   [−0.0718% +0.0012% +0.0858%] (p = 0.97 > 0.05)
                        thrpt:  [−0.0857% −0.0012% +0.0719%]
                        No change in performance detected.

simd/memset<u8>/136     time:   [3.6125 ns 3.6174 ns 3.6229 ns]
                        thrpt:  [34.961 GiB/s 35.014 GiB/s 35.062 GiB/s]
                 change:
                        time:   [−0.6087% −0.1314% +0.2680%] (p = 0.58 > 0.05)
                        thrpt:  [−0.2673% +0.1316% +0.6124%]
                        No change in performance detected.

simd/memset<u8>/1024    time:   [11.341 ns 11.346 ns 11.353 ns]
                        thrpt:  [84.002 GiB/s 84.055 GiB/s 84.092 GiB/s]
                 change:
                        time:   [−0.1288% −0.0636% +0.0134%] (p = 0.06 > 0.05)
                        thrpt:  [−0.0134% +0.0636% +0.1290%]
                        No change in performance detected.

simd/memset<u8>/131072  time:   [2.4705 µs 2.4717 µs 2.4733 µs]
                        thrpt:  [49.354 GiB/s 49.388 GiB/s 49.411 GiB/s]
                 change:
                        time:   [−0.2564% −0.0972% +0.0179%] (p = 0.20 > 0.05)
                        thrpt:  [−0.0179% +0.0973% +0.2570%]
                        No change in performance detected.

simd/memset<u8>/134217728
                        time:   [4.4030 ms 4.4104 ms 4.4190 ms]
                        thrpt:  [28.287 GiB/s 28.342 GiB/s 28.390 GiB/s]
                 change:
                        time:   [−0.0583% +0.1614% +0.3954%] (p = 0.17 > 0.05)
                        thrpt:  [−0.3938% −0.1611% +0.0583%]
                        No change in performance detected.

• LSX

simd/memset<u32>/8      time:   [2.3534 ns 2.4342 ns 2.5242 ns]
                        thrpt:  [2.9516 GiB/s 3.0608 GiB/s 3.1658 GiB/s]
                 change:
                        time:   [−19.116% −15.130% −11.603%] (p = 0.00 < 0.05)
                        thrpt:  [+13.126% +17.828% +23.633%]
                        Performance has improved.
simd/memset<u32>/136    time:   [7.0382 ns 7.0426 ns 7.0480 ns]
                        thrpt:  [17.971 GiB/s 17.985 GiB/s 17.996 GiB/s]
                 change:
                        time:   [−57.141% −57.110% −57.079%] (p = 0.00 < 0.05)
                        thrpt:  [+132.99% +133.15% +133.33%]
                        Performance has improved.

simd/memset<u32>/1024   time:   [30.019 ns 30.037 ns 30.060 ns]
                        thrpt:  [31.725 GiB/s 31.750 GiB/s 31.769 GiB/s]
                 change:
                        time:   [−71.652% −71.606% −71.575%] (p = 0.00 < 0.05)
                        thrpt:  [+251.80% +252.19% +252.76%]
                        Performance has improved.

simd/memset<u32>/131072 time:   [3.2877 µs 3.2897 µs 3.2923 µs]
                        thrpt:  [37.077 GiB/s 37.107 GiB/s 37.130 GiB/s]
                 change:
                        time:   [−74.960% −74.930% −74.885%] (p = 0.00 < 0.05)
                        thrpt:  [+298.17% +298.89% +299.36%]
                        Performance has improved.

simd/memset<u32>/134217728
                        time:   [4.4147 ms 4.4179 ms 4.4218 ms]
                        thrpt:  [28.269 GiB/s 28.294 GiB/s 28.314 GiB/s]
                 change:
                        time:   [−67.181% −67.149% −67.114%] (p = 0.00 < 0.05)
                        thrpt:  [+204.08% +204.41% +204.71%]
                        Performance has improved.

simd/memset<u8>/8       time:   [3.2016 ns 3.2031 ns 3.2052 ns]
                        thrpt:  [2.3245 GiB/s 2.3260 GiB/s 2.3271 GiB/s]
                 change:
                        time:   [−0.0666% +0.0051% +0.0807%] (p = 0.90 > 0.05)
                        thrpt:  [−0.0807% −0.0051% +0.0667%]
                        No change in performance detected.

simd/memset<u8>/136     time:   [3.6111 ns 3.6152 ns 3.6197 ns]
                        thrpt:  [34.991 GiB/s 35.035 GiB/s 35.075 GiB/s]
                 change:
                        time:   [−0.7119% −0.2467% +0.1774%] (p = 0.29 > 0.05)
                        thrpt:  [−0.1771% +0.2473% +0.7170%]
                        No change in performance detected.

simd/memset<u8>/1024    time:   [11.342 ns 11.349 ns 11.358 ns]
                        thrpt:  [83.962 GiB/s 84.030 GiB/s 84.082 GiB/s]
                 change:
                        time:   [−0.1126% −0.0288% +0.0686%] (p = 0.59 > 0.05)
                        thrpt:  [−0.0685% +0.0288% +0.1127%]
                        No change in performance detected.

simd/memset<u8>/131072  time:   [2.4707 µs 2.4723 µs 2.4742 µs]
                        thrpt:  [49.337 GiB/s 49.376 GiB/s 49.407 GiB/s]
                 change:
                        time:   [−0.2277% −0.0571% +0.0834%] (p = 0.52 > 0.05)
                        thrpt:  [−0.0833% +0.0571% +0.2282%]
                        No change in performance detected.

simd/memset<u8>/134217728
                        time:   [4.3991 ms 4.4057 ms 4.4138 ms]
                        thrpt:  [28.320 GiB/s 28.372 GiB/s 28.415 GiB/s]
                 change:
                        time:   [−0.1523% +0.0554% +0.2680%] (p = 0.62 > 0.05)
                        thrpt:  [−0.2673% −0.0554% +0.1525%]
                        No change in performance detected.