perf: complete render-cache adoption in PassPolarPlotControl

[g4dpz]

PR 8: Complete render-cache adoption in PassPolarPlotControl
Summary
Routes all per-frame Pen, Brush, and FormattedText allocations in PassPolarPlotControl through the existing _renderCache and a new _textCache, eliminating ~20 heap allocations per frame.

Changes
Added GetRoundCapPen(Color, double) to RenderResourceCache (with LineCap = Round, LineJoin = Round) for pass path segments
Segment loop: replaced new Pen(...) with _renderCache.GetRoundCapPen(color, 2.5)
DrawHorizonDisk: uses _renderCache.GetBrush(...) and _renderCache.GetPen(...)
DrawElevationRing: uses _renderCache.GetPen(...) / GetDashedPen(...) for dashed variant
DrawAzimuthSpokes: uses _renderCache.GetPen(palette.SkyPlotSpoke, 1)
DrawHoverMarker: uses _renderCache.GetBrush(...) and _renderCache.GetPen(...) for all three drawing calls
DrawCardinalLabels: added FormattedTextCache _textCache for N/E/S/W labels
Converted static drawing methods to instance methods for cache access
Clear() updated to include _roundCapPens dictionary
Testing
3 property-based tests: GetRoundCapPen returns same reference, has round cap/join, correct thickness/colour
2 unit tests: Clear() invalidates entries, different colours produce different pens
Full suite passes (1148 tests)
No behaviour change
Pixel-identical rendering output. The cache is purely an acceleration layer — same pens and brushes, just reused between frames.

[Copilot]

Pull request overview

Completes render-cache usage in PassPolarPlotControl by routing per-frame Brush/Pen allocations through RenderResourceCache and caching cardinal-direction FormattedText to reduce heap allocations during rendering.

Changes:

• Added RenderResourceCache.GetRoundCapPen(Color, double) and clears its cache via Clear().
• Updated PassPolarPlotControl drawing paths to use cached Brush/Pen instances (including round-cap pens for pass segments).
• Added FormattedTextCache usage for N/E/S/W labels and introduced a FormattedTextCache.Get(string, double, Color) overload.
• Added new unit/property tests validating GetRoundCapPen caching and configuration.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
OscarWatch/Controls/RenderResourceCache.cs	Adds round-cap pen caching and ensures it is cleared with other cached resources.
OscarWatch/Controls/PassPolarPlotControl.cs	Switches rendering to cached resources and adds formatted-text caching for cardinal labels.
OscarWatch/Controls/FormattedTextCache.cs	Adds overload to cache FormattedText using an explicit foreground Color.
OscarWatch.Tests/Performance/PassPolarPlotRenderCacheTests.cs	Adds tests covering round-cap pen caching correctness and cache invalidation.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.