Towards a single-file code export

Problem:

- Users may expect a single code file.
- Boilerplate is not versioned and changes may not be notified.

Solution:

- On export, prepend readme to generated.py
- Offer pyproject.toml as inline in generated.py, which is a new spec and supported by uv. It is kind of blocked as we use a github commit/branch for pytypid, but we can resolve this by publishing to pypi.
- Externalize boilerplate code as a library. See if it makes sense to put it as utilities into pytypid.

Result:

- one code file (generated.py)
- one license file
- possibly we'll still want to have a pyproject.toml for some reasons.