Avoid fixed-size long integral types for macOS

[knoepfel]

As mentioned in a Slack discussion:

The fixed-width integer type std::int64_t is a typedef (https://en.cppreference.com/w/cpp/types/integer.html).   In particular, std::int64_t on macOS is a typedef to long long.  So there is a mismatch between the long that the Python system expects, and the long long that is calculated by the type_id system.

This PR is to work around the problem until we have consistent treatment of types between C++ and Python.

[greenc-FNAL]

Review the full CodeQL report for details.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##             main     #449   +/-   ##
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  Coverage   84.90%   84.90%           
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  Files         127      127           
  Lines        3339     3339           
  Branches      575      575           
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  Hits         2835     2835           
  Misses        308      308           
  Partials      196      196           

Flag	Coverage Δ
unittests	84.90% <ø> (ø)

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Files with missing lines	Coverage Δ
plugins/python/src/modulewrap.cpp	76.69% <ø> (ø)

... and 3 files with indirect coverage changes

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[beojan]

This seems like it might be too restrictive actually, there might be other platform / libc combinations where int64_t isn't long.

In fact, if for some crazy reason someone's using a 32-bit platform, int64_t would be long long.

[beojan]

Thinking further, the generalization would be something like

if int64_t === long
    BASIC_CONVERTER(long, int64_t /* = long */...
else
    BASIC_CONVERTER(long, long ...
end

and then we might as well just have the versions without fixed-width types.

[knoepfel]

This seems like it might be too restrictive actually, there might be other platform / libc combinations where int64_t isn't long.

In fact, if for some crazy reason someone's using a 32-bit platform, int64_t would be long long.

Unconditionally requiring long to be int64_t is the over-restriction. This PR relaxes that restriction for macOS.

I agree there are other systems for which long and int64_t are not synonymous. This PR, however, is strictly a workaround: to enable continued Phlex development on macOS, not to support systems that are not currently used in our development, CI, or deployment.

A long-term solution will be the subject of another PR.

[wlav]

As discussed, fine for now. I'll reconsider when dealing with the refactoring and/or pull in the converters from a different place (pybind11 or cppyy) once we go to real data products.