Add comprehensive release process documentation

[vhaasteren]

Summary

This PR adds detailed documentation for the enterprise release process, which is fully automated but was not clearly documented.

Changes Made

• Added RELEASE.md: Comprehensive release documentation including:
  • Fully automated release process via GitHub Actions
  • Explanation of trusted publishing setup
  • Version management via setuptools_scm
  • Troubleshooting and release checklist
• Updated CONTRIBUTING.rst: Added "For Maintainers" section with link to release documentation

Release Process Documented

• Fully automated PyPI uploads via GitHub Actions
• Trusted publishing (no API tokens needed)
• Version management via setuptools_scm (automatic from git tags)
• GitHub environment configuration requirements

Benefits

• Clear understanding of the automated process
• Documentation of trusted publishing approach
• Easier troubleshooting when issues arise
• Better maintainer onboarding

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.59%. Comparing base (3668246) to head (bb064d5).
⚠️ Report is 37 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #427      +/-   ##
==========================================
- Coverage   72.61%   72.59%   -0.02%     
==========================================
  Files          13       13              
  Lines        3407     3478      +71     
==========================================
+ Hits         2474     2525      +51     
- Misses        933      953      +20     

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