Release v2.2.0

[igerber]

Summary

• Bump version to 2.2.0 across all version files
• Add CHANGELOG entry documenting:
  • Windows wheel builds using pure-Rust faer library
  • Rust backend migration from nalgebra/ndarray to faer
  • Numerical stability improvements and fallback handling
  • macOS CI compatibility for Python 3.14

Methodology references (required if estimator / math changes)

• Method name(s): N/A - version bump only, no methodology changes
• Paper / source link(s): N/A
• Any intentional deviations from the source (and why): None

Validation

• Tests added/updated: No test changes (tests were added in PR Add Windows wheel builds using faer pure Rust linear algebra #115)
• Backtest / simulation / notebook evidence (if applicable): N/A

Security / privacy

• Confirm no secrets/PII in this PR: Yes

Files Changed

• CHANGELOG.md - Added [2.2.0] release notes and comparison link
• diff_diff/__init__.py - __version__ = "2.2.0"
• pyproject.toml - version = "2.2.0"
• rust/Cargo.toml - version = "2.2.0"

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[github-actions]

Overall assessment: ✅ Looks good

Executive summary:

• Version bumped to 2.2.0 across package metadata; no functional code changes in this diff.
• Changelog adds the 2.2.0 release notes and comparison link.
• Registry review indicates no methodology cross-check required for this PR.

Methodology

• No findings. Registry reviewed; diff is version/changelog only with no estimator/inference logic changes.

Code Quality

• No findings.

Performance

• No findings.

Maintainability

• No findings.

Tech Debt

• No findings.

Security

• No findings.

Documentation/Tests

• No findings. Changelog updated; no tests changed for a version-only release.