feat: add AI Agent-driven test infrastructure (Phase 1)

Cherry-picked from copilot/add-new-feature-to-project branch (PR #24084):
- pkg/testinfra/types/ — Domain types
- pkg/testinfra/planner/ — Diff parser + path→test mapping
- pkg/testinfra/executor/ — Test execution interface
- pkg/testinfra/dedup/ — SQL fingerprinting & dedup
- cmd/mo-testplan/ — CLI tool
- .github/workflows/testplan.yaml — CI workflow

Agent-Logs-Url: https://github.com/matrixorigin/matrixone/sessions/01a80fb2-03a5-4645-8d55-6b07eada549b

Co-authored-by: Ariznawlll <108530700+Ariznawlll@users.noreply.github.com>

Author: Copilot