fix: compilation issues

solidity/contracts/DataReceiver.sol

@@ -59,19 +59,19 @@ contract DataReceiver is IDataReceiver, Governable {
       // NOTE: memory to storage is not supported
       // cachedObservations[_poolSalt][_poolNonce] = _observationsData;
       for (uint256 _i; _i < _observationsData.length; ++_i) {
-        cachedObservations[_poolSalt][_poolNonce].push(_observationsData[_i]);
+        _cachedObservations[_poolSalt][_poolNonce].push(_observationsData[_i]);
       }
       emit ObservationsCached(_poolSalt, _poolNonce, msg.sender);
       while (_currentNonce <= _poolNonce) {
         // Try backfilling pending observations (from current to {sent|first empty} nonce)
-        IOracleSidechain.ObservationData[] memory _cachedObservations = cachedObservations[_poolSalt][_currentNonce];
+        IOracleSidechain.ObservationData[] memory _cache = _cachedObservations[_poolSalt][_currentNonce];
         // If the struct is not empty, write it into the oracle
-        if (_cachedObservations.length > 0) {
+        if (_cache.length > 0) {
           // Since observation nonce == oracle nonce, we can safely write the observations
-          _oracle.write(_cachedObservations, _currentNonce);
-          emit ObservationsAdded(_poolSalt, _currentNonce, _cachedObservations, msg.sender);
+          _oracle.write(_cache, _currentNonce);
+          emit ObservationsAdded(_poolSalt, _currentNonce, _cache, msg.sender);
           // Clear out the written observations
-          delete cachedObservations[_poolSalt][_currentNonce];
+          delete _cachedObservations[_poolSalt][_currentNonce];
           _currentNonce++;
         } else {
           // When an empty nonce is found, break the loop