feat(highcharts): implement line-realtime (#3134)

## Implementation: `line-realtime` - highcharts

Implements the **highcharts** version of `line-realtime`.

**File:** `plots/line-realtime/implementations/highcharts.py`

**Parent Issue:** #3073

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20620593360)*

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

Author: github-actions[bot]

plots/line-realtime/metadata/highcharts.yaml

@@ -0,0 +1,19 @@
+# Per-library metadata for highcharts implementation of line-realtime
+# Auto-generated by impl-generate.yml
+
+library: highcharts
+specification_id: line-realtime
+created: '2025-12-31T14:12:42Z'
+updated: '2025-12-31T14:12:42Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20620593360
+issue: 3073
+python_version: 3.13.11
+library_version: unknown
+preview_url: https://storage.googleapis.com/pyplots-images/plots/line-realtime/highcharts/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/line-realtime/highcharts/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/line-realtime/highcharts/plot.html
+quality_score: null
+review:
+  strengths: []
+  weaknesses: []