test: add comprehensive tests for OracleDdlBuilder

- Add 34 tests for OracleDdlBuilder class covering all DDL operations
- Test buildCreateTableSql with various options (primary key, foreign keys, auto-increment, tablespace)
- Test buildDropTableSql and buildDropTableIfExistsSql
- Test column operations (add, drop, alter, rename)
- Test index operations (create, drop, rename, unique, fulltext, spatial)
- Test constraint operations (foreign keys, primary keys, unique, check)
- Test table rename operation
- Test formatColumnDefinition with various column schemas
- Test generateSequenceName method

Total: 34 new tests with 81 assertions.
Code coverage increased from 65.40% to 65.82% (Lines: 18164/27596).
All tests pass successfully.

Author: tommyknocker