feat(pygal): implement heatmap-geographic (#3647)

## Implementation: `heatmap-geographic` - pygal

Implements the **pygal** version of `heatmap-geographic`.

**File:** `plots/heatmap-geographic/implementations/pygal.py`

**Parent Issue:** #3638

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20885435790)*

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