Allow to override config parms in code/in config file

[johann-petrak]

Currently it causes an error if a parameter is specified both in the config file and the code.

It may be useful to just define a priority.

There are only few reasons why those parameters would get set in code:

• the code wants to make sure that a parameter is set specifically for the invocation
• the code sets a parameter that was e.g. chosen by a user during interaction
• the code knows the parameter has to be set in a specific context (e.g. temperature=1 if reasoning is used with Anthropic models)

So it is probably the better approach to give priority to parameter settings in the code!

[johann-petrak]

• Different models do or do not allow the "thinking=..." parameter: e.g. GPT5 will show an error if thinking is specified.
  • unsupported parms can get dropped using "drop_params=True"??? (check exact use!)
  • check: allowed_openai_params=['thinking']
• reasoning_content and thinking_blocks are returned for choice[0].message e.g. for Anthropic but not GPT5?