[Python SDK] ResultCache can deadlock the process

[pocesar]

Describe the bug

Due to how AgentFieldClient is mixing threading with asyncio, ResultCache can deadlock inside _await_execution_async + _await_execution_sync inside client.py

Related to #620

Steps to reproduce

1. Go to '...'
2. Run '...'
3. See error

Expected behavior

Screenshots / Logs

Environment

• Control plane version:
• SDK version (if applicable):
• Deployment environment (local, docker, kubernetes, etc.):

Additional context