P2: Formatter — add render handlers for Sequence DDL and SHOW/DESCRIBE statements

[ajitpratap0]

Problem

The formatter (pkg/formatter/render.go) is missing render handlers for several statement types, which causes round-trip failures: you can parse these statements but cannot format them back to SQL.

Missing Handlers

Statement Type	Dialect	Impact
CreateSequenceStatement	PostgreSQL, Oracle, MariaDB (v1.14.0)	Cannot format sequence DDL
AlterSequenceStatement	PostgreSQL, Oracle, MariaDB	Cannot format sequence modifications
DropSequenceStatement	PostgreSQL, Oracle, MariaDB	Cannot format sequence drops
ShowStatement	MySQL, MariaDB, ClickHouse	Cannot format SHOW DATABASES/TABLES/CREATE
DescribeStatement	MySQL, MariaDB, PostgreSQL (\d)	Cannot format DESCRIBE/\d table

Impact

Parse → transform → format workflows fail silently (returns empty string or error) for:

CREATE SEQUENCE order_id START 1 INCREMENT 1 MINVALUE 1 MAXVALUE 9999999 CACHE 10;
ALTER SEQUENCE order_id RESTART WITH 100;
DROP SEQUENCE IF EXISTS order_id;
SHOW TABLES LIKE 'user%';
DESCRIBE users;

Implementation

Add to pkg/formatter/render.go:

case *ast.CreateSequenceStatement:
    return r.renderCreateSequence(stmt)

case *ast.AlterSequenceStatement:
    return r.renderAlterSequence(stmt)

case *ast.DropSequenceStatement:
    return r.renderDropSequence(stmt)

case *ast.ShowStatement:
    return r.renderShow(stmt)

case *ast.DescribeStatement:
    return r.renderDescribe(stmt)

Acceptance Criteria

• CreateSequenceStatement renders correctly (all options: START, INCREMENT, MINVALUE, MAXVALUE, CACHE, CYCLE/NO CYCLE)
• AlterSequenceStatement renders correctly
• DropSequenceStatement renders correctly (with IF EXISTS)
• ShowStatement renders correctly for all variants (SHOW TABLES, SHOW DATABASES, SHOW CREATE TABLE, SHOW PROCESSLIST)
• DescribeStatement renders correctly
• Round-trip test: parse → format → parse → compare ASTs (identity)
• Keyword casing respects formatter options
• Tests for all new handlers: 5+ per statement type