feat(pygal): implement pie-drilldown (#3132)

## Implementation: `pie-drilldown` - pygal

Implements the **pygal** version of `pie-drilldown`.

**File:** `plots/pie-drilldown/implementations/pygal.py`

**Parent Issue:** #3072

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20620564803)*

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