Add check for graph validity before commuting conditional gates in squashing passes #6326

Job	Run time
Check tket library version	17s
Build and test pytket (ubuntu)	13m 31s
Build and test pytket (macos) (macos-13)	10m 12s
Build and test pytket (windows)	14m 15s
Build and test pytket (macos) (macos-15)	10m 28s
Build and test (tket) (ubuntu-24.04)	3m 16s
Build and test (tket) (windows-2022)	5m 29s
Build and test (tket) (macos-13)	4m 14s
Build and test (tket) (macos-15)	1m 59s
Check documentation build	54s
Check C++ code formatting	24s
Check pytket line and branch coverage	9s
Publish pytket coverage	0s
All build and test jobs successful (or skipped)	1s
	1h 5m 9s

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