Create binary wheels with mypyc

[hukkin]

Based on @ofek's (who I'll add as co-author) PR #165.

This creates mypyc binary wheels while keeping flit_core as default build backend (which was my concern earlier #165 (comment)). CI switches to setuptools only for creating binary wheels. The idea is to keep flit_core as default until Python 3.11 EOL date, after which TOML parser bootstrapping is no longer a concern.

User visible changes here are:

• slightly different TypeError messages from binary wheels (with mypyc we lose control over the exact message)
• TOMLDecodeError shows as tomli._parser.TOMLDecodeError: in tracebacks instead of tomli.TOMLDecodeError:. The hack that changes the exception's __module__ is not accepted by mypyc
• type[DEPRECATED_DEFAULT] shows in TOMLDecodeError's type hint

The changes seem acceptable to me.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (443a0c1) to head (6dd93ff).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #242   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          527       529    +2     
  Branches        97        97           
=========================================
+ Hits           527       529    +2     

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[hukkin]

I think this needs protection against stack overflow (inline arrays and tables).