Update to use `uv init`

This tool current defines the repo structure and the contents of the `pyproject.toml` in a fairly inflexible manner.

Since the only packaging option is now `uv`, we should consider using the `uv init` command to create the repo structure. This will allow more flexibility in the types of software that can be built (libraries, executables, packages, etc)

### Proposed approach

1. Continue to use cookiecutter for configurable options and non-python package files (pre-commit, `.github/`, etc)
2. In the post-gen hooks script:
1. Run `uv init` using configurable options selected in the cookiecutter command.
2. Add the extra config to the generated `pyproject.toml` (mypy, ruff, pytest, etc)
3. Keep existing approach of adding dependencies

Start with the post-generation hook and the existing cookiecutter handling for repository structure and pyproject.toml. Trace how configurable options and dependencies are currently applied, then generate representative library and executable projects to verify that uv init creates the structure and the extra mypy, ruff, and pytest configuration is preserved.

Written by the indexing model from the issue text.