support for gpt5 models

[e-strauss]

this minor fix enables the usage of gpt5 like models, which do not support temperature values by allowing null values in the config for the temperature value for models.

example usage:

python -m aide.run data_dir="input" \
  goal="make nice a ml pipeline" \
  agent.code.model="gpt-5.2-codex" \
  agent.code.temp=null

[dexhunter]

Hi @e-strauss thanks for the contribution! Btw feel free to try out the weco-cli with more advanced features

[dexhunter]

lgtm