Fix several bugs related to macro expansions

[cschreib]

This PR does the following:

• Fixes Fix support for expressions containing commas in check macros #61
• Fixes Suspicious static_assert condition in get_format_code() #66
• Fixes REQUIRE_THAT and CHECK_THAT do not work #67
• Fixes REQUIRE_THROWS_MATCHES and CHECK_THROWS_MATCHES do not preserve matcher state #68

[codecov-commenter]

Codecov Report

Merging #69 (e0f3c48) into main (8dc9f62) will not change coverage.
The diff coverage is n/a.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main      #69   +/-   ##
=======================================
  Coverage   92.56%   92.56%           
=======================================
  Files           2        2           
  Lines        1049     1049           
=======================================
  Hits          971      971           
  Misses         78       78           

Impacted Files	Coverage Δ
include/snitch/snitch.hpp	96.06% <ø> (ø)
src/snitch.cpp	90.95% <ø> (ø)

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