Add `internal` feature for `validate_num_of_signers` (#740) #1319

Job	Run time
build with default features	29s
build with MSRV (1.66.1)	1m 38s
build with no_std (ristretto255)	22s
build with no_std (ed25519)	24s
test on beta	2m 3s
actionlint	6s
build with no_std (p256)	24s
build with no_std (secp256k1)	27s
Clippy	36s
Check Rust doc	38s
build with no_std (rerandomized)	18s
Rustfmt	11s
Check if automatically generated code is up to date	23s
	7m 59s

Provide feedback