feat: Enhance PostgreSQL type handling and migration scripts

- Introduced equivalent base types and variants for PostgreSQL types to normalize type comparisons.
- Added functions for normalizing SQL types and retrieving equivalent type variants.
- Updated migration writer to handle type alterations with checks for existing types.
- Implemented logic to create necessary extensions (e.g., pg_trgm) based on schema requirements.
- Enhanced tests to cover new functionality for type normalization and migration handling.
- Improved handling of GIN indexes to use appropriate operator classes based on column types.

cmd/relspec/testhelpers_test.go

@@ -71,6 +71,40 @@ func writeTestJSON(t *testing.T, path string, tableNames []string) {
 	}
 }
 
+func writeTestJSONWithSingleColumnType(t *testing.T, path, tableName, columnType string) {
+	t.Helper()
+
+	db := minimalDatabase{
+		Name: "test_db",
+		Schemas: []minimalSchema{{
+			Name: "public",
+			Tables: []minimalTable{{
+				Name:   tableName,
+				Schema: "public",
+				Columns: map[string]minimalColumn{
+					"id": {
+						Name:          "id",
+						Table:         tableName,
+						Schema:        "public",
+						Type:          columnType,
+						NotNull:       true,
+						IsPrimaryKey:  true,
+						AutoIncrement: true,
+					},
+				},
+			}},
+		}},
+	}
+
+	data, err := json.Marshal(db)
+	if err != nil {
+		t.Fatalf("failed to marshal test JSON: %v", err)
+	}
+	if err := os.WriteFile(path, data, 0644); err != nil {
+		t.Fatalf("failed to write test file %s: %v", path, err)
+	}
+}
+
 // convertState captures and restores all convert global vars.
 type convertState struct {
 	sourceType    string