Add backend-aware test parameter scaling for pure Python CI

[igerber]

Summary

• Add CIParams class and ci_params session-scoped pytest fixture in conftest.py that detects pure Python mode and scales down bootstrap iterations and TROP grid sizes
• Update ~89 test functions across 7 test files to use ci_params.bootstrap(n) for bootstrap iteration counts and ci_params.grid(values) for TROP lambda grids
• Make 11 hardcoded assertion values dynamic to match scaled parameters
• Leave API-only tests (no .fit() calls) and warning-threshold tests unchanged

Methodology references (required if estimator / math changes)

• N/A - no methodology changes. Only test parameter scaling; same code paths exercised with fewer iterations in pure Python mode.

Validation

• Tests added/updated: tests/conftest.py, tests/test_trop.py, tests/test_staggered.py, tests/test_wild_bootstrap.py, tests/test_sun_abraham.py, tests/test_estimators.py, tests/test_methodology_callaway.py, tests/test_methodology_did.py
• All 387+ tests across modified files pass with Rust backend
• With Rust backend, all values pass through unchanged (zero behavior change)

Security / privacy

• Confirm no secrets/PII in this PR: Yes

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[github-actions]

Overall assessment: ⚠️ Needs changes

Executive summary:

• P1: The TROP paper-conformance test now accepts as few as 11 successful bootstrap draws even when n_boot=30, weakening the regression guard for stratified sampling.
• P2: Bootstrap scaling in pure Python mode reduces methodology convergence tests to ~35 iterations, which can make SE-convergence assertions noisy and less meaningful.
• No estimator or inference logic changes detected in this diff; methodology registry requirements appear unchanged.
• AGENTS.md not found in repo; proceeded without additional agent instructions.

Methodology

• Severity: P1 | Impact: The paper-conformance test for stratified bootstrap now allows as few as 11 successful draws even when n_boot=30, which weakens detection of regressions in Algorithm 3’s stratified sampling behavior. | Concrete fix: Make the threshold proportional to n_boot (e.g., >= max(11, int(0.67 * n_boot)) or >= n_boot - 5) so Rust-backend runs keep the stronger expectation while pure Python scaling remains feasible. tests/test_trop.py:L1615-L1669
• Severity: P3 | Impact: No estimator/assumption/inference code paths were changed in this diff; registry requirements are unaffected. | Concrete fix: None. docs/methodology/REGISTRY.md:L1-L40

Code Quality

• Severity: P3 | Impact: No code-quality issues identified in the changed test/fixture code beyond findings above. | Concrete fix: None.

Performance

• Severity: P3 | Impact: Changes are test-only performance optimizations; no production performance impact observed. | Concrete fix: None.

Maintainability

• Severity: P3 | Impact: No maintainability issues introduced beyond findings above. | Concrete fix: None.

Tech Debt

• Severity: P3 | Impact: No new tech-debt concerns introduced in this diff. | Concrete fix: None.

Security

• Severity: P3 | Impact: No security-sensitive changes or secrets observed in the diff. | Concrete fix: None.

Documentation/Tests

• Severity: P2 | Impact: Methodology convergence tests now use ci_params.bootstrap(499), which scales to ~35 iterations in pure Python mode; this can make the 20–25% SE-convergence assertions noisy and reduce methodological verification strength. | Concrete fix: Exempt these convergence tests from scaling (keep high n_boot), or conditionally relax/skip when n_boot falls below a minimum threshold. tests/conftest.py:L99-L113, tests/test_methodology_callaway.py:L803-L839