Disable 32-bit Python builds

[darbyjohnston]

Fixes #1788

This PR disables x86 builds to help reduce CI time and troubleshooting.

Marking this as WIP to test the changes.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.61%. Comparing base (c0e97b0) to head (2f3fb87).
⚠️ Report is 59 commits behind head on main.

❌ Your changes status has failed because you have indirect coverage changes. Learn more about Unexpected Coverage Changes and reasons for indirect coverage changes.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1789      +/-   ##
==========================================
- Coverage   84.11%   81.61%   -2.51%     
==========================================
  Files         198      176      -22     
  Lines       22241    12335    -9906     
  Branches     4687     3024    -1663     
==========================================
- Hits        18709    10067    -8642     
+ Misses       2610     1725     -885     
+ Partials      922      543     -379     

Flag	Coverage Δ
py-unittests	81.61% <ø> (-2.51%)	⬇️

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see 67 files with indirect coverage changes

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[darbyjohnston]

According to the documentation x86 is built by default on Windows and Linux:
https://cibuildwheel.pypa.io/en/stable/options/#archs

This change specifies to only build x86_64/AMD64.

[darbyjohnston]

Marking this as "ready for review" as discussed at the last TSC meeting.

So far there have been no responses to the OTIO slack post by @meshula that 32-bit builds are needed.