feat!: `used_extensions` calls for both ops and signatures #2856

Job	Run time
Check for changes	6s
tests (Rust nightly, coverage)	4m 41s
check	2m 10s
Build benchmarks 🏋️	3m 30s
tests (Rust 1.75)	4m 9s
tests (Rust stable, all features)	3m 4s
tests (Rust stable, no features)	2m 28s
tests (Rust beta)	3m 25s
tests hugr-llvm	0s
Check standard extensions	11s
Required checks 🦀	1s
	23m 45s

Provide feedback