Summary

• add TypeValidator.default_expr(expression) to support raw SQL default expressions
• emit raw DEFAULT <expression> in datasource generation when default_expr is used
• update migration emitter to fall back to .default_expr(...) for non-literal datasource defaults (for example generateUUIDv4())
• add parity tests for type modifiers, datasource generation, and migrate output
• bump package version from 0.1.2 to 0.1.3

Verification

• .venv/bin/pytest tests/test_phase1_schema_generator_parity.py tests/test_phase4_migrate_runner_emitter_parity.py tests/test_migrate_parity.py
• .venv/bin/pytest