fix: use stable sort for migration operations (fixes #15)

Replace List.Sort() with OrderBy() in TimescaleMigrationsModelDiffer to preserve the ependency order from base.GetDifferences(). The unstable sort was causing CreateIndex operations to appear before CreateTable operations, breaking migrations.

Added comprehensive tests for operation ordering including a regression test with 30+ operations that reliably fails with unstable sort.

Author: sebastian-ederer

src/Eftdb/Internals/TimescaleMigrationsModelDiffer.cs

@@ -37,9 +37,8 @@ public override IReadOnlyList<MigrationOperation> GetDifferences(IRelationalMode
             }
 
             // Sort the entire list based on the priority defined in the helper method
-            allOperations.Sort((op1, op2) => GetOperationPriority(op1).CompareTo(GetOperationPriority(op2)));
-
-            return allOperations;
+            List<MigrationOperation> sortedOperations = [.. allOperations.OrderBy(GetOperationPriority)];
+            return sortedOperations;
         }
 
         /// <summary>