Clean up TODO.md: remove resolved items, update line counts

[igerber]

Summary

• Remove 7 resolved tech debt entries that were cluttering the table
• Update all module line counts (power.py now 2588, staggered.py 2275, linalg.py 2289)
• Remove stale EfficientDiD docs TODO — tutorial and API docs already exist
• Add Status column to feature gaps table linking to Survey Phase 7a/7b
• Promote Plotly kwargs issue to top of Testing/Docs section
• Flag power.py for potential splitting (largest file at 2588 lines)

Methodology references (required if estimator / math changes)

• N/A — no methodology changes

Validation

• Tests added/updated: No test changes (documentation only)
• Backtest / simulation / notebook evidence: N/A

Security / privacy

• Confirm no secrets/PII in this PR: Yes

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[github-actions]

Overall Assessment

✅ Looks good

Executive Summary

• The diff is limited to TODO.md; it does not change estimator code, weighting, variance formulas, identification checks, or defaults.
• The updated large-file counts in TODO.md match the current package files, e.g. diff_diff/power.py, diff_diff/linalg.py, diff_diff/staggered.py, and diff_diff/trop.py.
• The removed “resolved” methodology/debt items are backed by current implementation and registry entries, including replicate-weight survey df in diff_diff/survey.py, CallawaySantAnna survey support in diff_diff/staggered.py and docs/methodology/REGISTRY.md, the ContinuousDiD anticipation filter in diff_diff/continuous_did.py, and the EfficientDiD Hausman cluster-count fix in diff_diff/efficient_did.py.
• P3 informational: the new Survey Phase 7a/7b labels in TODO.md, TODO.md, and TODO.md are not defined elsewhere in-repo, so the new status column is less traceable than it could be.
• I could not execute tests in this environment because pytest is not installed.

Methodology

No findings. This PR only updates tracking text, and the deleted methodology-related TODO rows appear genuinely resolved in the current code/registry: diff_diff/survey.py, diff_diff/staggered.py, diff_diff/continuous_did.py, diff_diff/efficient_did.py, and docs/methodology/REGISTRY.md.

Code Quality

No findings. The refreshed module-size table in TODO.md is consistent with the current file sizes I checked.

Performance

No findings. The PR does not alter runtime behavior; it only updates tracked performance debt text.

Maintainability

• Severity: P3. Impact: The new Survey Phase 7a/7b labels in TODO.md, TODO.md, and TODO.md are not tied to an issue, roadmap section, or in-file definition, so future reviewers cannot resolve those statuses from repo context alone. Concrete fix: replace those labels with a concrete issue/roadmap reference, or add a short section defining Phase 7a/7b in ROADMAP.md or TODO.md.

Tech Debt

No findings. Removing resolved entries looks accurate given the current helper consolidation in diff_diff/results.py and the presence of current EfficientDiD API docs in docs/api/efficient_did.rst.

Security

No findings.

Documentation/Tests

No findings on the cleanup itself. Existing tests cover several removed resolved items, including the EfficientDiD Hausman fix in tests/test_efficient_did.py, ContinuousDiD anticipation filtering in tests/test_continuous_did.py, full-design CallawaySantAnna bootstrap in tests/test_survey_phase4.py, TROP Rao-Wu support in tests/test_survey_phase5.py, and replicate-IF variance coverage in tests/test_survey_phase6.py. Residual gap: I could not run the suite locally because pytest is unavailable in this environment.