feat: configurable verification pipeline (timeouts, checks, ordering)

[omsherikar]

Problem

Verification behavior is mostly hard-coded:

• TestSuiteGate uses a fixed 45s subprocess timeout.
• Default check list and order are fixed in VerificationEngine.__init__.
• No first-class way to disable e.g. the test gate in slow CI without code changes.

Impact

Teams cannot tune safety vs speed for their repo size, CI tier, or policy (e.g. "syntax + imports only" in quick PR checks).

Suggested direction

• Extend RefactronConfig (or a nested verification: section in YAML) with: enabled checks, ordering, test_gate_timeout_sec, optional pytest_extra_args.
• Thread config into VerificationEngine / CLI (refactron verify, refactron autofix --verify, refactron run).
• Document defaults and migration for existing users.

References

• refactron/verification/engine.py
• refactron/verification/checks/test_gate.py (timeout=45)