Dont allow observing a write

Author: wickwirew

Sources/Feather/FeatherError.swift

@@ -26,4 +26,5 @@ public enum FeatherError: Error {
     case decodingError(String)
     case encodingError(String)
     case requiredAssociationFailed(parent: String, childKey: String)
+    case cannotObserveWriteQuery
 }

Sources/Feather/QueryObservation.swift

@@ -61,6 +61,10 @@ public final class DatabaseQueryObservation<Query>: DatabaseSubscriber, QueryObs
         }
 
         do {
+            guard query.transactionKind != .write else {
+                throw FeatherError.cannotObserveWriteQuery
+            }
+            
             let output = try await query.execute(with: input)
             onChange(output)
         } catch {