ImputationDiD methodology validation (PR-B): exact FE variance + unit-clustered Eq.8 + R parity #2371

Job	Run time
Pure Python Fallback	1h 21m 45s
Rust Unit Tests (ubuntu-latest)	1m 24s
Rust Unit Tests (windows-latest)	2m 33s
Rust Unit Tests (macos-latest)	1m 11s
Rust Unit Tests (ubuntu-24.04-arm)	1m 34s
Python Tests (ubuntu-24.04-arm, py3.11)	40m 38s
Python Tests (ubuntu-latest, py3.13)	1h 7m 35s
Python Tests (ubuntu-24.04-arm, py3.14)	41m 44s
Python Tests (ubuntu-latest, py3.11)	1h 1m 21s
Python Tests (macos-latest, py3.13)	32m 14s
Python Tests (macos-latest, py3.11)	33m 58s
Python Tests (windows-latest, py3.13)	1h 6m 17s
Python Tests (macos-latest, py3.14)	34m 32s
Python Tests (ubuntu-24.04-arm, py3.13)	41m 16s
Python Tests (ubuntu-latest, py3.14)	52m 1s
Python Tests (windows-latest, py3.14)	1h 1m 14s
Python Tests (windows-latest, py3.11)	59m 3s
	11h 20m 20s

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