feat!: `used_extensions` calls for both ops and signatures #2826

Job	Run time
Check for changes	8s
tests (Rust stable, no features)	56s
Build benchmarks 🏋️	2m 3s
tests (Rust stable, all features)	1m 4s
check	59s
tests (Rust nightly, coverage)	2m 49s
tests (Rust 1.75)	58s
tests (Rust beta)	59s
tests hugr-llvm	0s
Check standard extensions	0s
Required checks 🦀	1s
	9m 57s

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