Is `cookiecutter` needed at runtime by end-users?
**Is your feature request related to a problem? Please describe.**

`Cookiecutter` doesn't seem to be needed at runtime.

**Describe the solution you'd like**

Use an [extras](https://peps.python.org/pep-0508/#extras) dependency (i.e. `pip install "nimporter[cli]"`) in `pyproject.toml` for library authors to access the functionality.

**Describe alternatives you've considered**

Alternative is leaving it as is which means extra dependencies for end-users. Though maybe there is some component outside the CLI that requires `cookiecutter` I'm missing.

**Additional context**

There is a non-trivial list of `cookiecutter` dependencies:
```
cookiecutter 2.1.1 A command-line utility that creates projects from project templates, e.g. creating a Python package project from a Python package project template.
├── binaryornot >=0.4.4
│   └── chardet >=3.0.2
├── click >=7.0,<9.0.0
│   ├── colorama *
│   └── importlib-metadata *
│       ├── typing-extensions >=3.6.4
│       └── zipp >=0.5
├── jinja2 >=2.7,<4.0.0
│   └── markupsafe >=2.0
├── jinja2-time >=0.2.0
│   ├── arrow *
│   │   ├── python-dateutil >=2.7.0
│   │   │   └── six >=1.5
│   │   └── typing-extensions *
│   └── jinja2 *
│       └── markupsafe >=2.0
├── python-slugify >=4.0.0
│   └── text-unidecode >=1.3
├── pyyaml >=5.3.1
└── requests >=2.23.0
    ├── certifi >=2017.4.17
    ├── charset-normalizer >=2,<4
    ├── idna >=2.5,<4
    └── urllib3 >=1.21.1,<1.27
```

Keeping `nimporter` deps slim may be inline with library authors wanting lightweight extension modules.

Thanks for the awesome work melding `python` and `nim`!