feat: enhance workflow management with cycle detection and audit logging

[nikunjkumar05]

Fix #4462

Summary

Fixes runtime workflow graph expansion validation before workflow execution begins.

Changes

• Added workflow transition tracking and a WorkflowGraphExpander.
• Rejects invalid runtime graph transitions before lifecycle state changes.
• Detects duplicate transitions, unknown step transitions, self-cycles, and graph cycles.
• Preserves workflow and step lifecycle state when invalid expansion is rejected.
• Records redacted audit decisions and graph expansion metrics.
• Added deterministic regression tests for cyclic runtime expansion rejection and valid execution.
• Avoided eager package imports that pulled in platform-specific modules during test/import discovery.

Verification

• python -m compileall src tests passed.
• Import smoke check passed for workflow, scheduler, engine, agent, and orchestrator modules.
• Manual regression smoke checks passed for:
  • cyclic graph rejection before execution
  • lifecycle state preservation
  • redacted audit/log decision
  • valid graph execution
  • scheduler priority behavior