feat(datafusion): support alter column

[QuakeWang]

Purpose

DataFusion SQL supports adding, dropping, and renaming columns, but rejects ALTER COLUMN even though the core schema layer already supports type and nullability changes.

This change exposes the existing schema evolution capabilities through SQL while preserving schema and primary-key index consistency.

Brief change log

• Support ALTER COLUMN ... TYPE and SET DATA TYPE.
• Support SET NOT NULL and DROP NOT NULL.
• Preserve existing nullability for type-only changes.
• Reject unsupported conversion expressions and non-atomic mixed ALTER operations.
• Prevent destructive changes to primary-key vector and full-text index columns.

Tests

• Added SQL mapping and validation unit tests.
• Added a filesystem catalog integration test.
• Added primary-key index schema guard tests.
• Passed formatting, Clippy, and affected test suites.

API and Format

Adds DataFusion SQL DDL support. No storage format changes.

Documentation

Updated the supported SQL statement list.

[JingsongLi]

+1