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/merge.go

@@ -258,6 +258,11 @@ func runMerge(cmd *cobra.Command, args []string) error {
 	fmt.Fprintf(os.Stderr, "      ✓ Merge complete\n\n")
 	fmt.Fprintf(os.Stderr, "%s\n", merge.GetMergeSummary(result))
 
+	if strings.EqualFold(mergeOutputType, "pgsql") && len(result.TypeConflicts) > 0 {
+		return fmt.Errorf("merge detected conflicting existing column types and cannot safely continue with pgsql output\n%s",
+			merge.GetColumnTypeConflictSummary(result, 10))
+	}
+
 	// Step 4: Write output
 	fmt.Fprintf(os.Stderr, "\n[4/4] Writing output...\n")
 	fmt.Fprintf(os.Stderr, "      Format: %s\n", mergeOutputType)