Implement crypto byte array newtypes in term of a shared type (#3684)

Introduces `CryptoBytes` type defined as:

```rust
pub struct CryptoBytes<const N: usize, Tag = ()>(pub [u8; N], PhantomData<fn() -> Tag>);
```

The type implements a bunch of methods and traits which are typically
expected from a byte array newtype
(NOTE: some of the methods and trait implementations IMO are a bit
redundant, but I decided to maintain them all to not change too much
stuff in this PR)

It also introduces two (generic) typical consumers of `CryptoBytes`:
`PublicBytes` and `SignatureBytes`.

```rust
pub struct PublicTag;
pub PublicBytes<const N: usize, CryptoTag> = CryptoBytes<N, (PublicTag, CryptoTag)>;

pub struct SignatureTag;
pub SignatureBytes<const N: usize, CryptoTag> = CryptoBytes<N, (SignatureTag, CryptoTag)>;
```

Both of them use a tag to differentiate the two types at a higher level.
Downstream specializations will further specialize using a dedicated
crypto tag. For example in ECDSA:


```rust
pub struct EcdsaTag;

pub type Public = PublicBytes<PUBLIC_KEY_SERIALIZED_SIZE, EcdsaTag>;
pub type Signature = PublicBytes<PUBLIC_KEY_SERIALIZED_SIZE, EcdsaTag>;
```

Overall we have a cleaner and most importantly **consistent** code for
all the types involved

All these details are opaque to the end user which can use `Public` and
`Signature` for the cryptos as before

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-westend/tests/tests.rs

@@ -81,12 +81,7 @@ fn construct_extrinsic(
 	);
 	let payload = SignedPayload::new(call.clone(), extra.clone()).unwrap();
 	let signature = payload.using_encoded(|e| sender.sign(e));
-	UncheckedExtrinsic::new_signed(
-		call,
-		account_id.into(),
-		Signature::Sr25519(signature.clone()),
-		extra,
-	)
+	UncheckedExtrinsic::new_signed(call, account_id.into(), Signature::Sr25519(signature), extra)
 }
 
 fn construct_and_apply_extrinsic(