Bump version to 2.5.0

[igerber]

Summary

• Bump version to 2.5.0 across all version files (__init__.py, pyproject.toml, Cargo.toml)
• Add CHANGELOG entry for v2.5.0 documenting Stacked DiD estimator (Wing et al. 2024)

Methodology references (required if estimator / math changes)

• N/A — version bump only, no methodology changes

Validation

• Tests added/updated: No test changes (version bump only)
• Backtest / simulation / notebook evidence (if applicable): N/A

Security / privacy

• Confirm no secrets/PII in this PR: Yes

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Generated with Claude Code

[github-actions]

Overall assessment: ✅ Looks good

Executive summary

• Version bump to 2.5.0 is consistent across Python package metadata, library export, and Rust crate. (pyproject.toml:L5-L8, diff_diff/__init__.py:L156, rust/Cargo.toml:L1-L4)
• Changelog adds a 2.5.0 release entry and compare link. (CHANGELOG.md:L8-L22, CHANGELOG.md:L811-L812)
• No estimator logic or inference code is modified in this PR; methodology and edge-case checklists are not implicated.

Methodology

• No issues found.

Code Quality

• No issues found.

Performance

• No issues found.

Maintainability

• No issues found.

Tech Debt

• No issues found.

Security

• No issues found.

Documentation/Tests

• Severity: P3
  Impact: Test coverage not re-validated for the release bump.
  Concrete fix: Run the standard test suite before release tagging.