Langroid

Minor:
* RedisCache: only warn _first_ time about missing pw
* Task: do not actually create cache (of type RedisCache) in definition; use classmethod to only create when first used -- this fixes Redis-related warnings that were shown simply when doing `import langroid as lr`

Task: Restore old logic of process_invalid_step_result(): insert a DO-NOT-KNOW response if not valid response found in step.

* Improve Task infinite loop check to handle repeats like A 1 B 1 C 1 A 1 B 1 C 1 etc
* Task - do not create dummy NO_ANSWER response when step has no response (i.e. pending message does not change)
* Task - fix llm model displayed, to use agent.llm.config not agent.config.llm
* Switch examples to default to gpt-4o
* Task - when sub-task receives a msg, make deep copy, not modify orig

For ollama models, allow `api_base` to be set via OpenAIGPTConfig()