Update remappings.txt for upgradeable contracts and set up submodule (#4639)

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Ernesto García <ernestognw@gmail.com>

contracts/proxy/utils/UUPSUpgradeable.sol

@@ -15,8 +15,6 @@ import {ERC1967Utils} from "../ERC1967/ERC1967Utils.sol";
  * `UUPSUpgradeable` with a custom implementation of upgrades.
  *
  * The {_authorizeUpgrade} function must be overridden to include access restriction to the upgrade mechanism.
- *
- * @custom:stateless
  */
 abstract contract UUPSUpgradeable is IERC1822Proxiable {
     /// @custom:oz-upgrades-unsafe-allow state-variable-immutable

contracts/token/ERC1155/utils/ERC1155Holder.sol

@@ -11,8 +11,6 @@ import {IERC1155Receiver} from "../IERC1155Receiver.sol";
  *
  * IMPORTANT: When inheriting this contract, you must include a way to use the received tokens, otherwise they will be
  * stuck.
- *
- * @custom:stateless
  */
 abstract contract ERC1155Holder is ERC165, IERC1155Receiver {
     /**

contracts/token/ERC721/utils/ERC721Holder.sol

@@ -11,8 +11,6 @@ import {IERC721Receiver} from "../IERC721Receiver.sol";
  * Accepts all token transfers.
  * Make sure the contract is able to use its token with {IERC721-safeTransferFrom}, {IERC721-approve} or
  * {IERC721-setApprovalForAll}.
- *
- * @custom:stateless
  */
 abstract contract ERC721Holder is IERC721Receiver {
     /**

contracts/utils/Context.sol

@@ -12,8 +12,6 @@ pragma solidity ^0.8.20;
  * is concerned).
  *
  * This contract is only required for intermediate, library-like contracts.
- *
- * @custom:stateless
  */
 abstract contract Context {
     function _msgSender() internal view virtual returns (address) {

contracts/utils/Multicall.sol

@@ -7,8 +7,6 @@ import {Address} from "./Address.sol";
 
 /**
  * @dev Provides a function to batch together multiple calls in a single external call.
- *
- * @custom:stateless
  */
 abstract contract Multicall {
     /**

contracts/utils/introspection/ERC165.sol

@@ -16,8 +16,6 @@ import {IERC165} from "./IERC165.sol";
  *     return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
  * }
  * ```
- *
- * @custom:stateless
  */
 abstract contract ERC165 is IERC165 {
     /**