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.

pkg/writers/pgsql/templates/alter_column_type.tmpl

@@ -1,2 +1,2 @@
 ALTER TABLE {{qual_table .SchemaName .TableName}}
-  ALTER COLUMN {{quote_ident .ColumnName}} TYPE {{.NewType}};
+  ALTER COLUMN {{quote_ident .ColumnName}} TYPE {{.NewType}}{{if .UsingExpr}} USING {{.UsingExpr}}{{end}};

pkg/writers/pgsql/templates/alter_column_type_with_check.tmpl

@@ -0,0 +1,22 @@
+DO $$
+DECLARE
+  current_type text;
+BEGIN
+  SELECT pg_catalog.format_type(a.atttypid, a.atttypmod)
+    INTO current_type
+  FROM pg_attribute a
+  JOIN pg_class t ON t.oid = a.attrelid
+  JOIN pg_namespace n ON n.oid = t.relnamespace
+  WHERE n.nspname = '{{.SchemaName}}'
+    AND t.relname = '{{.TableName}}'
+    AND a.attname = '{{.ColumnName}}'
+    AND a.attnum > 0
+    AND NOT a.attisdropped;
+
+  IF current_type IS NOT NULL
+     AND current_type <> ALL(ARRAY[{{.EquivalentTypes}}]) THEN
+    ALTER TABLE {{qual_table .SchemaName .TableName}}
+      ALTER COLUMN {{quote_ident .ColumnName}} TYPE {{.NewType}}{{if .UsingExpr}} USING {{.UsingExpr}}{{end}};
+  END IF;
+END;
+$$;