Add Staggered Triple Difference estimator #679

Job	Run time
Rust Unit Tests (macos-latest)	1m 28s
Python Tests (ubuntu-24.04-arm, py3.13)	18m 54s
Rust Unit Tests (ubuntu-24.04-arm)	1m 48s
Python Tests (ubuntu-latest, py3.11)	39m 45s
Python Tests (macos-latest, py3.13)	18m 41s
Python Tests (ubuntu-24.04-arm, py3.11)	18m 36s
Python Tests (windows-latest, py3.11)	36m 51s
Rust Unit Tests (windows-latest)	2m 18s
Python Tests (macos-latest, py3.11)	19m 17s
Pure Python Fallback	1h 0m 27s
Python Tests (windows-latest, py3.13)	37m 15s
Python Tests (ubuntu-latest, py3.13)	40m 23s
Rust Unit Tests (ubuntu-latest)	1m 19s
	4h 57m 2s

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