feat!: `used_extensions` calls for both ops and signatures #2792

Job	Run time
Check for changes	4s
tests (Rust stable, all features)	3m 7s
tests (Rust stable, no features)	2m 19s
Build benchmarks 🏋️	2m 31s
check	1m 32s
tests (Rust nightly, coverage)	4m 26s
tests (Rust 1.75)	3m 35s
tests (Rust beta)	2m 54s
tests hugr-llvm	0s
Check standard extensions	5s
Required checks 🦀	1s
	20m 34s

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