evm: Emit events when updating inbound and outbound limits (#546)

* Add `OutboundTransferLimitUpdated` and `InboundTransferLimitUpdated` events
* Emit these events when `_setOutboundLimit` and `_setInboundLimit` are called respectively

Author: nvsriram

evm/src/interfaces/IRateLimiterEvents.sol

@@ -25,4 +25,19 @@ interface IRateLimiterEvents {
     event OutboundTransferRateLimited(
         address indexed sender, uint64 sequence, uint256 amount, uint256 currentCapacity
     );
+
+    /// @notice Emitted when the outbound transfer limit is updated.
+    /// @dev Topic0
+    ///      0x7e3b0fc388be9d36273f66210aed83be975df3a9adfffa4c734033f498f362cd.
+    /// @param oldLimit The old outbound limit.
+    /// @param newLimit The new outbound limit.
+    event OutboundTransferLimitUpdated(uint256 oldLimit, uint256 newLimit);
+
+    /// @notice Emitted when the inbound transfer limit is updated.
+    /// @dev Topic0
+    ///      0x739ed886fd81a3ddc9f4b327ab69152e513cd45b26fda0c73660eaca8e119301.
+    /// @param chainId The chain ID the limit is set for.
+    /// @param oldLimit The old inbound limit.
+    /// @param newLimit The new inbound limit.
+    event InboundTransferLimitUpdated(uint16 indexed chainId, uint256 oldLimit, uint256 newLimit);
 }

evm/src/libraries/RateLimiter.sol

@@ -96,7 +96,11 @@ abstract contract RateLimiter is IRateLimiter, IRateLimiterEvents {
     function _setOutboundLimit(
         TrimmedAmount limit
     ) internal virtual {
-        _setLimit(limit, _getOutboundLimitParamsStorage());
+        RateLimitParams storage rateLimitParams = _getOutboundLimitParamsStorage();
+        TrimmedAmount oldLimit = rateLimitParams.limit;
+        uint8 decimals = tokenDecimals();
+        _setLimit(limit, rateLimitParams);
+        emit OutboundTransferLimitUpdated(oldLimit.untrim(decimals), limit.untrim(decimals));
     }
 
     function getOutboundLimitParams() public pure virtual returns (RateLimitParams memory) {
@@ -116,7 +120,13 @@ abstract contract RateLimiter is IRateLimiter, IRateLimiterEvents {
     }
 
     function _setInboundLimit(TrimmedAmount limit, uint16 chainId_) internal virtual {
-        _setLimit(limit, _getInboundLimitParamsStorage()[chainId_]);
+        RateLimitParams storage rateLimitParams = _getInboundLimitParamsStorage()[chainId_];
+        TrimmedAmount oldLimit = rateLimitParams.limit;
+        uint8 decimals = tokenDecimals();
+        _setLimit(limit, rateLimitParams);
+        emit InboundTransferLimitUpdated(
+            chainId_, oldLimit.untrim(decimals), limit.untrim(decimals)
+        );
     }
 
     function getInboundLimitParams(