fix(rust): deterministic clustered vcov — first-appearance cluster aggregation #2791

Job	Run time
Pure Python Fallback	1h 18m 4s
Python Tests (ubuntu-24.04-arm, py3.11)	33m 38s
Python Tests (windows-latest, py3.14)	43m 35s
Rust Unit Tests (windows-latest)	2m 30s
Rust Unit Tests (ubuntu-latest)	1m 22s
Python Tests (ubuntu-24.04-arm, py3.14)	32m 17s
Python Tests (windows-latest, py3.13)	1h 2m 49s
Rust Unit Tests (ubuntu-24.04-arm)	1m 28s
Rust Unit Tests (macos-latest)	1m 13s
Python Tests (windows-latest, py3.11)	42m 0s
Python Tests (ubuntu-24.04-arm, py3.13)	32m 4s
Python Tests (macos-latest, py3.14)	34m 22s
Python Tests (macos-latest, py3.11)	28m 12s
Python Tests (macos-latest, py3.13)	31m 56s
Python Tests (ubuntu-latest, py3.14)	1h 6m 46s
Python Tests (ubuntu-latest, py3.11)	1h 3m 25s
Python Tests (ubuntu-latest, py3.13)	1h 1m 41s
	10h 17m 22s

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