Add Staggered Triple Difference estimator #683

Job	Run time
Rust Unit Tests (ubuntu-24.04-arm)	1m 27s
Python Tests (windows-latest, py3.11)	36m 49s
Python Tests (macos-latest, py3.13)	19m 22s
Pure Python Fallback	1h 0m 5s
Rust Unit Tests (macos-latest)	1m 32s
Python Tests (ubuntu-latest, py3.13)	40m 42s
Python Tests (macos-latest, py3.11)	16m 35s
Python Tests (ubuntu-24.04-arm, py3.13)	18m 41s
Python Tests (windows-latest, py3.13)	37m 22s
Rust Unit Tests (windows-latest)	2m 26s
Rust Unit Tests (ubuntu-latest)	1m 28s
Python Tests (ubuntu-latest, py3.11)	40m 28s
Python Tests (ubuntu-24.04-arm, py3.11)	18m 30s
	4h 55m 27s

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