fix: migrate dev/test/docs tooling from Poetry extras to dependency groups

Fixes #1097 — fresh clone setup fails because 'poetry install --extras dev'
does not reliably install dev tools like pytest-cases.

Changes:
- pyproject.toml: move dev/test/docs deps from [tool.poetry.dependencies]
  + [tool.poetry.extras] into proper Poetry dependency groups
  ([tool.poetry.group.dev/test/docs.dependencies])
- .github/actions/setup-python/action.yaml: use '--with dev,test,docs'
  instead of '--extras dev'
- CONTRIBUTING.md: update install command and add note about groups
- poetry.lock: regenerated for new group structure

Author: khushthecoder

.github/actions/setup-python/action.yaml

@@ -19,4 +19,4 @@ runs:
       shell: bash
       run: |
         poetry env use ${{ inputs.python-version }}
-        poetry install --extras dev
+        poetry install --with dev,test,docs

CONTRIBUTING.md

@@ -52,9 +52,13 @@ Both of these can be installed using your distribution's package manager or [Hom
 
    ```bash
    poetry env use 3.12
-   poetry install --extras dev
+   poetry install --with dev,test,docs
    ```
 
+   This installs the runtime dependencies along with the `dev`, `test`, and `docs`
+   [dependency groups](https://python-poetry.org/docs/managing-dependencies/#dependency-groups).
+   If you only need to run tests, `poetry install --with test` is sufficient.
+
    **Recommended**: Use `poetry run` to run commands inside the virtual environment:
 
    ```bash