new tests for step send_to_llm and small fixes

[oleks-dev]

Add New Tests for send_to_llm Step

• Goal: Validate the send_to_llm function's behavior across different configurations, including:
  • Normal operation with default and custom providers.
  • Error handling (e.g., empty prompts, invalid provider modes).
  • Output control (e.g., verbose, quiet, and final output modes).

Code Fixes

• Rename step_sent_to_llm.py to step_send_to_llm.py
• Add more checks for config.settings elements when they are not set