Make DatabasePreUpdateEvent.Kind Sendable, matching DatabaseEvent.Kind, and also duplicate comments from DatabaseEvent.Kind while here

Author: Jason-Abbott

GRDB/Core/TransactionObserver.swift

@@ -1231,16 +1231,16 @@ private struct CopiedDatabaseEventImpl: DatabaseEventImpl {
 
 public struct DatabasePreUpdateEvent {
 
-    /// An event kind
-    public enum Kind: CInt {
-        /// SQLITE_INSERT
-        case insert = 18
+    /// An event kind.
+    public enum Kind: CInt, Sendable {
+        /// An insertion event
+        case insert = 18 // SQLITE_INSERT
 
-        /// SQLITE_DELETE
-        case delete = 9
+        /// A deletion event
+        case delete = 9 // SQLITE_DELETE
 
-        /// SQLITE_UPDATE
-        case update = 23
+        /// An update event
+        case update = 23 // SQLITE_UPDATE
     }
 
     /// The event kind