Support Feasibility Polishing in Python Interface.

[Lhongpei]

• Add a test script.
• Add the option in README.
• Add parameters of fp in the param dict to support fp.

[ZedongPeng]

Do we also need to update the static py::dict get_default_params_py() function? @LucasBoTang
https://github.com/MIT-Lu-Lab/cuPDLPx/blob/d45b339cf72c52612cc3df30c4e79fc11e1537de/python_bindings/_core_bindings.cpp#L205C1-L240C2

[LucasBoTang]

Do we also need to update the static py::dict get_default_params_py() function? @LucasBoTang https://github.com/MIT-Lu-Lab/cuPDLPx/blob/d45b339cf72c52612cc3df30c4e79fc11e1537de/python_bindings/_core_bindings.cpp#L205C1-L240C2

Yes, we should update get_default_params_py() as well to keep it consistent with the C++ defaults.

[ZedongPeng]

Output

$ pytest test/test_feasibility_polishing.py 
.                                                                                                                                                                                              [100%]
1 passed in 1.95s
Solution Summary
  Status        : OPTIMAL
  Iterations    : 330
  Solve time    : 0.016 sec
  Primal obj    : 3.000347287
  Dual obj      : 3.000194279
  Primal infeas : 1.819e-05
  Dual infeas   : 4.879e-05
Feasibility Polishing Summary
  Primal Status        : FEAS_POLISH_SUCCESS
  Primal Iterations    : 610
  Primal Time Usage    : 0.0183 sec
  Dual Status          : FEAS_POLISH_SUCCESS
  Dual Iterations      : 610
  Dual Time Usage      : 0.0203 sec
  Primal Residual      : 2.069e-11
  Dual Residual        : 7.729e-11
  Primal Dual Gap      : 2.562e-04