Move ITs into their own crate #602

Job	Run time
Check formatting	18s
Validate minimal dependency versions	1m 7s
Check clippy	1m 22s
Run integration tests (5)	1m 9s
Run integration tests (2025)	1m 3s
Run unit tests (macOS-latest)	1m 39s
Run unit tests (ubuntu-latest)	1m 6s
Run integration tests (4.4)	57s
Run unit tests (windows-latest)	3m 28s
Release	0s
	12m 9s

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