feat(highcharts): implement stereonet-equal-area (#4919)

## Implementation: `stereonet-equal-area` - highcharts

Implements the **highcharts** version of `stereonet-equal-area`.

**File:** `plots/stereonet-equal-area/implementations/highcharts.py`

**Parent Issue:** #4576

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/23121188982)*

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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]