Allow providing options in alias or model definition

[mqudsi]

It would be very convenient to allow defining an alias such as o3-mini-high that is an alias for o3-mini but also automatically supplies -o reasoning high. In particular, it makes it easier to use shell completions and to swap out one model for the other when testing a different response to the previously executed llm shell command from bash/shell history (only edit the -m payload and not have to also add or remove 3 additional arguments, especially if you're comparing, say, o3-mini-medium vs gemini-2.5 vs o3-mini-high or whatever where it's not the same base model).

Alternatively, if it could be defined in a models .yaml instead of in the alias.yaml as a separate model, for example

- model_id: o3-mini-high
  model_name: o3-mini
  model_args:
  - reasoning: high

- model_id: o3-mini-medium
  model_name: o3-mini
  model_args:
  - reasoning: medium