feat!: `used_extensions` calls for both ops and signatures #2836

Job	Run time
Check for changes	7s
check	1m 17s
Build benchmarks 🏋️	1m 56s
tests (Rust 1.75)	2m 43s
tests (Rust stable, no features)	1m 15s
tests (Rust stable, all features)	1m 59s
tests (Rust beta)	2m 18s
tests (Rust nightly, coverage)	4m 29s
tests hugr-llvm	0s
Check standard extensions	8s
Required checks 🦀	1s
	16m 13s

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