Add SyntheticControl estimator (classic SCM, Abadie-Diamond-Hainmueller 2010) — PR-1 core #2256

Job	Run time
Python Tests (ubuntu-latest, py3.13)	1h 3m 15s
Rust Unit Tests (windows-latest)	2m 18s
Rust Unit Tests (ubuntu-latest)	1m 20s
Python Tests (macos-latest, py3.13)	31m 39s
Python Tests (ubuntu-latest, py3.14)	1h 8m 44s
Python Tests (windows-latest, py3.11)	54m 13s
Python Tests (macos-latest, py3.14)	34m 35s
Python Tests (macos-latest, py3.11)	31m 21s
Python Tests (ubuntu-latest, py3.11)	1h 1m 11s
Rust Unit Tests (macos-latest)	1m 22s
Rust Unit Tests (ubuntu-24.04-arm)	1m 19s
Python Tests (ubuntu-24.04-arm, py3.11)	42m 53s
Pure Python Fallback	4h 22m 18s
Python Tests (ubuntu-24.04-arm, py3.13)	43m 39s
Python Tests (windows-latest, py3.14)	1h 7m 1s
Python Tests (ubuntu-24.04-arm, py3.14)	44m 19s
Python Tests (windows-latest, py3.13)	55m 0s
	14h 26m 27s

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