Add Free Threading support to CI

[nateprewitt]

Description of changes:
The primary blocker for supporting free threading in Boto3/Botocore/Smithy Python was support in the upstream dependency, awscrt. Starting in awscrt 0.32.0 (awslabs/aws-crt-python#725), releases began distributing artifacts for Python 3.13t and 3.14t. While 3.13t was released as experimental, 3.14t is starting to gain adoption.

Given there are no remaining blockers, this PR adds beta support for free threaded builds and makes sure that contract is validated in CI.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[TingDaoK]

shipit!!!!!

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.71%. Comparing base (8647a30) to head (2f2eee8).
⚠️ Report is 16 commits behind head on develop.
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #391      +/-   ##
===========================================
+ Coverage    80.28%   80.71%   +0.42%     
===========================================
  Files           16       16              
  Lines         3013     3012       -1     
===========================================
+ Hits          2419     2431      +12     
+ Misses         594      581      -13     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.