fix(build): respect .python-version when generating pyenv

[iamllama]

ref: https://forums.ankiweb.net/t/anki-build-failed-because-python-3-14-is-installed-on-my-system-in-addition-to-python-3-13/67484?u=llama

Mirrors what we do in the launcher: https://github.com/ankitects/anki/blob/55691fc254a61e1d982873720b20ee6c4b852111/qt/launcher/src/main.rs?plain=1#L336-L346

before:

DEBUG Acquired lock for `/anki`
DEBUG Ignoring Python version file at `.python-version` due to `--no-config`
DEBUG Using Python request `>=3.9` from `requires-python` metadata
DEBUG Checking for Python environment at `out/pyenv`

after:

DEBUG Acquired lock for `/anki`
DEBUG Using Python request `3.13.5` from explicit request
DEBUG Checking for Python environment at `out/pyenv`
DEBUG The project environment's Python version satisfies the request: `Python 3.13.5`

[bradhilton]

@corbt _openai_client_config.engine_args does not initialize the engine, so this is unsurprising. Instead engine args have to be specified with TrainableModel._internal_config. The reason why we also have engine_args here is because the OpenAI-compatible API server looks at some of these arguments. This API is really sub-optimal and probably best solved by unifying all args under register, or potentially a new API, something like deploy.

[corbt]

Thanks, that's helpful. Yes definitely in favor of simplifying the API here!