[marketplace] Move RequestState enum to Requests.sol

contracts/Marketplace.sol

@@ -365,14 +365,6 @@ contract Marketplace is Collateral, Proofs, StateRetrieval {
     return s == RequestState.New || s == RequestState.Started;
   }
 
-  enum RequestState {
-    New, // [default] waiting to fill slots
-    Started, // all slots filled, accepting regular proofs
-    Cancelled, // not enough slots filled before expiry
-    Finished, // successfully completed
-    Failed // too many nodes have failed to provide proofs, data lost
-  }
-
   struct RequestContext {
     uint256 slotsFilled;
     RequestState state;

contracts/Requests.sol

@@ -37,6 +37,14 @@ struct PoR {
   bytes name; // random name
 }
 
+enum RequestState {
+  New, // [default] waiting to fill slots
+  Started, // all slots filled, accepting regular proofs
+  Cancelled, // not enough slots filled before expiry
+  Finished, // successfully completed
+  Failed // too many nodes have failed to provide proofs, data lost
+}
+
 library Requests {
   function id(Request memory request) internal pure returns (RequestId) {
     return RequestId.wrap(keccak256(abi.encode(request)));