Fix live dot shine-through while series is dimmed

[brandtnewlabs]

Summary

• fade live dots and pulse rings out whenever seriesOpacity dims replacement data, then fade them back in once the series is fully opaque
• apply the behavior consistently to LiveChart and LiveChartSeries while keeping strokes, fills, value lines, labels, axes, and badges on their existing opacity paths
• add a permanent Dim while loading control to the Line & area example; it pauses the synthetic feed and chart window while dimmed, then reseeds replacement history on completion
• add regression tests, API/guide documentation, and a changelog entry

Root cause

The live-dot groups used seriesOpacity directly. At partial opacity, Skia composited a translucent dot over its own line, so the stroke showed through the dot and the pulse remained visibly active. The indicator group now uses a discrete UI-thread target with a short fade: hidden for any dimmed series, visible again only at full opacity.

Before and after

Both clips use the Line & area example and hold the chart at 50% opacity long enough to show the pulse behavior. In the updated example, the dimmed range remains frozen for the whole loading interval and a fresh current range replaces it on completion.

Before	After
Download before video (MP4)	Download after video (MP4)

Verification

• npm run verify — 103 suites passed, 1,576 tests passed, 5 skipped
• npx react-doctor@latest --verbose --diff — no issues in changed React files
• iOS Simulator manual validation of the fade-out, dimmed hold, and fade-in sequence