Resolve: Update state variables that could be declared immutable as immutable #605 (#609)

* Turn vars to immutable

* Make vars immutable

Author: nkrishang

contracts/base/Staking1155Base.sol

@@ -46,7 +46,7 @@ import { CurrencyTransferLib } from "../lib/CurrencyTransferLib.sol";
 
 contract Staking1155Base is ContractMetadata, Multicall, Ownable, Staking1155, ERC165, IERC1155Receiver {
     /// @dev ERC20 Reward Token address. See {_mintRewards} below.
-    address public rewardToken;
+    address public immutable rewardToken;
 
     /// @dev The address of the native token wrapper contract.
     address internal immutable nativeTokenWrapper;

contracts/base/Staking20Base.sol

@@ -45,7 +45,7 @@ import { CurrencyTransferLib } from "../lib/CurrencyTransferLib.sol";
 
 contract Staking20Base is ContractMetadata, Multicall, Ownable, Staking20 {
     /// @dev ERC20 Reward Token address. See {_mintRewards} below.
-    address public rewardToken;
+    address public immutable rewardToken;
 
     /// @dev Total amount of reward tokens in the contract.
     uint256 private rewardTokenBalance;

contracts/base/Staking721Base.sol

@@ -46,10 +46,10 @@ import { CurrencyTransferLib } from "../lib/CurrencyTransferLib.sol";
 
 contract Staking721Base is ContractMetadata, Multicall, Ownable, Staking721, ERC165, IERC721Receiver {
     /// @dev ERC20 Reward Token address. See {_mintRewards} below.
-    address public rewardToken;
+    address public immutable rewardToken;
 
     /// @dev The address of the native token wrapper contract.
-    address public nativeTokenWrapper;
+    address public immutable nativeTokenWrapper;
 
     /// @dev Total amount of reward tokens in the contract.
     uint256 private rewardTokenBalance;

contracts/extension/Staking1155.sol

@@ -15,7 +15,7 @@ abstract contract Staking1155 is ReentrancyGuard, IStaking1155 {
     //////////////////////////////////////////////////////////////*/
 
     ///@dev Address of ERC1155 contract -- staked tokens belong to this contract.
-    address public stakingToken;
+    address public immutable stakingToken;
 
     /// @dev Flag to check direct transfers of staking tokens.
     uint8 internal isStaking = 1;

contracts/extension/Staking721.sol

@@ -15,7 +15,7 @@ abstract contract Staking721 is ReentrancyGuard, IStaking721 {
     //////////////////////////////////////////////////////////////*/
 
     ///@dev Address of ERC721 NFT contract -- staked tokens belong to this contract.
-    address public stakingToken;
+    address public immutable stakingToken;
 
     /// @dev Flag to check direct transfers of staking tokens.
     uint8 internal isStaking = 1;

contracts/infra/ContractPublisher.sol

@@ -30,7 +30,7 @@ contract ContractPublisher is IContractPublisher, ERC2771Context, AccessControlE
 
     /// @notice Whether the contract publisher is paused.
     bool public isPaused;
-    IContractPublisher public prevPublisher;
+    IContractPublisher public immutable prevPublisher;
 
     /*///////////////////////////////////////////////////////////////
                                 Mappings