Bump version to 2.4.1

[igerber]

Summary

• Bump version to 2.4.1 in __init__.py, pyproject.toml, and rust/Cargo.toml
• Add CHANGELOG entry for v2.4.1 covering module splits, safe_inference migration, tutorial additions, and bug fixes
• Add comparison link for v2.4.1

Methodology references (required if estimator / math changes)

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

Validation

• Tests added/updated: No test changes
• Backtest / simulation / notebook evidence: N/A

Security / privacy

• Confirm no secrets/PII in this PR: Yes

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[github-actions]

Overall assessment: ⚠️ Needs changes

Executive Summary

• Version bump is consistent across Python package, Rust crate, and __version__ (pyproject.toml:L7, rust/Cargo.toml:L3, diff_diff/__init__.py:L151).
• No estimator/math/variance code changes in this diff, so no methodology registry cross-check was triggered.
• The 2.4.1 changelog lists substantial code/estimator changes not present in this PR; please confirm or trim to avoid misleading release notes (CHANGELOG.md:L8-L21).

Methodology
No findings. This diff only updates versions and release notes; no estimator implementations, assumptions, or variance/SE logic were modified.

Code Quality
No findings.

Performance
No findings.

Maintainability
No findings.

Tech Debt
No findings.

Security
No findings.

Documentation/Tests

• P2 — Impact: The 2.4.1 changelog lists module splits, inference migration, and estimator-related fixes that are not part of this PR; if those changes are not already merged and included in the 2.4.1 release, the changelog will misrepresent the release contents. Concrete fix: Confirm those items are already in the release branch/tag for 2.4.1, or trim the 2.4.1 entry to only the changes included in this release. CHANGELOG.md:L8-L21