fix: remove unused constants and add gap (#1519)

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**Motivation:**

Fix missing gap and cleanup unused constants

**Modifications:**

*Describe the modifications you've done.*

**Result:**

*After your change, what will change.*

Author: 8sunyuan

src/contracts/multichain/ECDSACertificateVerifierStorage.sol

@@ -50,4 +50,11 @@ abstract contract ECDSACertificateVerifierStorage is IECDSACertificateVerifier {
     ) {
         operatorTableUpdater = _operatorTableUpdater;
     }
+
+    /**
+     * @dev This empty reserved space is put in place to allow future versions to add new
+     * variables without shifting down storage in the inheritance chain.
+     * See https://docs.openzeppelin.com/contracts/4.x/upgradeable#storage_gaps
+     */
+    uint256[45] private __gap;
 }

src/contracts/permissions/KeyRegistrarStorage.sol

@@ -5,14 +5,6 @@ import "../interfaces/IAllocationManager.sol";
 import "../interfaces/IKeyRegistrar.sol";
 
 abstract contract KeyRegistrarStorage is IKeyRegistrar {
-    // Constants
-
-    /// @dev Gas limit for pairing operations to prevent DoS
-    uint256 internal constant PAIRING_EQUALITY_CHECK_GAS = 400_000;
-
-    /// @dev Hash of zero ECDSA public key (0x04 + 64 zero bytes)
-    bytes32 internal constant ZERO_ECDSA_PUBKEY_HASH = keccak256(abi.encodePacked(bytes1(0x04), new bytes(64)));
-
     // Immutables
 
     /// @dev Reference to the AllocationManager contract