Handle SASA pickling failures on Python 3.14

[Marcello-Sega]

Summary

• unpicklable class problems surfaced using python 3.14
• switch SASA multiprocessing setup to use a multiprocessing context + use a static function to avoid the pickling issue
• catch pickling and process errors, falling back to single-core execution in unhandled cases, raising a warning

[chatgpt-codex-connector]

Codex usage limits have been reached for code reviews. Please check with the admins of this repo to increase the limits by adding credits.
Credits must be used to enable repository wide code reviews.

[codecov]

Codecov Report

❌ Patch coverage is 82.30088% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.88%. Comparing base (4707acb) to head (203a2b2).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pytim/sasa.py	82.30%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #512      +/-   ##
==========================================
- Coverage   86.25%   85.88%   -0.38%     
==========================================
  Files          52       52              
  Lines        3849     3882      +33     
==========================================
+ Hits         3320     3334      +14     
- Misses        529      548      +19     

☔ 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.