Bump version to 2.3.2

[igerber]

Summary

• Bump version from 2.3.1 to 2.3.2 across all version files (__init__.py, pyproject.toml, rust/Cargo.toml)
• Add CHANGELOG entry for v2.3.2 covering Python 3.13 support, Sun-Abraham methodology fixes, and SyntheticDiD tutorial improvements

Methodology references (required if estimator / math changes)

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

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 bumped consistently to 2.3.2 across Python package metadata and Rust crate metadata. diff_diff/__init__.py:L145, pyproject.toml:L5-L8, rust/Cargo.toml:L1-L4
• Changelog updated with the 2.3.2 release notes. CHANGELOG.md:L8-L24
• No estimator, inference, or math code changes in this PR; scope is release metadata only. diff_diff/__init__.py:L145, pyproject.toml:L5-L8, rust/Cargo.toml:L1-L4

Methodology
No findings. This PR only updates versions and release notes; no estimator/methodology code is changed.

Code Quality
No findings.

Performance
No findings.

Maintainability
No findings.

Tech Debt
No findings.

Security
No findings.

Documentation/Tests
No findings.