added ProofState

proofs.proto

@@ -2,10 +2,26 @@ syntax = "proto3";
 
 package cashu.v1;
 option go_package = "gen/go/cashurpc";
+/*
+A proof can be in one of the following states
+
+A proof is UNSPENT if it has not been spent yet
+A proof is PENDING if it is being processed in a transaction (in an ongoing payment). A PENDING proof cannot be used in another transaction until it is live again.
+A proof is SPENT if it has been redeemed and its secret is in the list of spent secrets of the mint.
+
+ */
+
+enum ProofState {
+  unspecified = 0;
+  UNSPENT = 1;
+  PENDING = 2;
+  SPENT = 3;
+}
 
 message Proof {
   uint64 amount = 1;
   string id = 2;
   string secret = 3;
   string C = 4;
+  ProofState state = 5;
 }