contracts-bedrock: fix some compiler warnings (#2839)

also regenerate `op-bindings`

.changeset/nice-meals-visit.md

+---
+'@eth-optimism/contracts-bedrock': patch
+---
+
+Reduce the number of compiler warnings

packages/contracts-bedrock/.gas-snapshot

@@ -11,8 +11,8 @@ GasBenchMark_OptimismPortal:test_depositTransaction_benchmark_1() (gas: 35328)
 CrossDomainHashing_Test:test_l2TransactionHash() (gas: 104131)
 DeployerWhitelist_Test:test_owner() (gas: 7625)
 DeployerWhitelist_Test:test_storageSlots() (gas: 33461)
-GasPriceOracle_Test:test_baseFee() (gas: 8373)
-GasPriceOracle_Test:test_gasPrice() (gas: 8384)
+GasPriceOracle_Test:test_baseFee() (gas: 8370)
+GasPriceOracle_Test:test_gasPrice() (gas: 8381)
 GasPriceOracle_Test:test_l1BaseFee() (gas: 10626)
 GasPriceOracle_Test:test_onlyOwnerSetDecimals() (gas: 10553)
 GasPriceOracle_Test:test_onlyOwnerSetOverhead() (gas: 10599)

packages/contracts-bedrock/contracts/L1/L1StandardBridge.sol

@@ -113,7 +113,7 @@ contract L1StandardBridge is StandardBridge, Initializable {
      *
      * @return Address of the corresponding L2 bridge contract.
      */
-    function l2TokenBridge() external returns (address) {
+    function l2TokenBridge() external view returns (address) {
         return address(otherBridge);
     }
 

packages/contracts-bedrock/contracts/L2/GasPriceOracle.sol

@@ -70,7 +70,7 @@ contract GasPriceOracle is Ownable {
      *
      * @return Current L2 gas price (base fee).
      */
-    function gasPrice() public returns (uint256) {
+    function gasPrice() public view returns (uint256) {
         return block.basefee;
     }
 
@@ -79,7 +79,7 @@ contract GasPriceOracle is Ownable {
      *
      * @return Current L2 base fee.
      */
-    function baseFee() public returns (uint256) {
+    function baseFee() public view returns (uint256) {
         return block.basefee;
     }
 

packages/contracts-bedrock/contracts/L2/L2CrossDomainMessenger.sol

@@ -34,7 +34,7 @@ contract L2CrossDomainMessenger is CrossDomainMessenger {
      *
      * @return Address of the L1CrossDomainMessenger contract.
      */
-    function l1CrossDomainMessenger() public returns (address) {
+    function l1CrossDomainMessenger() public view returns (address) {
         return otherMessenger;
     }
 

packages/contracts-bedrock/contracts/libraries/Burn.sol

@@ -31,7 +31,7 @@ library Burn {
      *
      * @param _amount Amount of gas to burn.
      */
-    function gas(uint256 _amount) internal {
+    function gas(uint256 _amount) internal view {
         uint256 i = 0;
         uint256 initialGas = gasleft();
         while (initialGas - gasleft() < _amount) {