Fixes new clippy lints on the latest nightly

[kaczmarczyck]

Now that we can use a later toolchain, we see more lints. Overlaps with #580 , but I didn't reproduce all lints. Missing are all changes like:

-                large_blob_data.extend(&[0x0C, 0x00]);
+                large_blob_data.extend([0x0C, 0x00]);

Not sure what toolchain version these are coming from.

On a side note, other libraries still have lints that need to be fixed on the current nightly.

[coveralls]

Coverage: 96.176% (+0.1%) from 96.058% when pulling b5b8cce on kaczmarczyck:clippy-lints into ca65902 on google:develop.