chore: change `setup.py` to use optional build_ext option

[CaselIT]

This allows skipping the compilation of the c file if it fails for some reason, like the compiler is missing. The build will still fail if cython can't generate the c file from the py/pyx file but that should be ok.

The optional keyword is documented here https://setuptools.pypa.io/en/latest/userguide/ext_modules.html#setuptools.Extension

optional (bool) – specifies that a build failure in the extension should not abort the build process, but simply not install the failing extension.

Fixes: #2237

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (6ba54b4) to head (5c70ac4).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2242 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 63 63 Lines 6852 6852 Branches 1260 1260 ========================================= Hits 6852 6852 ```

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[CaselIT]

Thanks. Will merge with master soon!

[CaselIT]

updated