Add introduction tag for v5.1 contracts (#5228)

Co-authored-by: Ernesto García <ernestognw@gmail.com>

contracts/utils/cryptography/Hashes.sol

@@ -4,6 +4,8 @@ pragma solidity ^0.8.20;
 
 /**
  * @dev Library of standard hash functions.
+ *
+ * _Available since v5.1._
  */
 library Hashes {
     /**

contracts/utils/cryptography/P256.sol

@@ -14,6 +14,8 @@ import {Errors} from "../Errors.sol";
  * Based on the original https://github.com/itsobvioustech/aa-passkeys-wallet/blob/d3d423f28a4d8dfcb203c7fa0c47f42592a7378e/src/Secp256r1.sol[implementation of itsobvioustech] (GNU General Public License v3.0).
  * Heavily inspired in https://github.com/maxrobot/elliptic-solidity/blob/c4bb1b6e8ae89534d8db3a6b3a6b52219100520f/contracts/Secp256r1.sol[maxrobot] and
  * https://github.com/tdrerup/elliptic-curve-solidity/blob/59a9c25957d4d190eff53b6610731d81a077a15e/contracts/curves/EllipticCurve.sol[tdrerup] implementations.
+ *
+ * _Available since v5.1._
  */
 library P256 {
     struct JPoint {

contracts/utils/cryptography/RSA.sol

@@ -11,6 +11,8 @@ import {Math} from "../math/Math.sol";
  * RSA semantically secure for signing messages.
  *
  * Inspired by https://github.com/adria0/SolRsaVerify/blob/79c6182cabb9102ea69d4a2e996816091d5f1cd1[Adrià Massanet's work] (GNU General Public License v3.0).
+ *
+ * _Available since v5.1._
  */
 library RSA {
     /**