refactor: code to pass ruff check

-   Modify `pyproject.toml` to exclude `plotly/graph_objs` from checking for now.
-   Modify `pyproject.toml` to include `anywidget` in core dependencies
    (because `plotly/basewidget.py` needs it).
-   Clean up several hundred complaints from `ruff` about unused variables and imports.
-   Clean up cases in `tests/**/*.py` where the same function name was used for several tests
    (which meant that only the last one defined was actually run).
-   Reformat code after recent changes.

Author: gvwilson

.circleci/config.yml

@@ -153,7 +153,7 @@ jobs:
             source .venv/bin/activate
             uv sync --extra dev_core
       - run:
-          name: Check formatting with ruff
+          name: Check handwritten code with ruff
           command: |
             source .venv/bin/activate
             ruff check .