Add typed video-quality selection to the options menu of all three skins

[Ortes]

Stacked on #963 — the first commit here is that PR; review only the last commit(s). Rebase this branch once #963 lands.

What this adds

A typed, host-driven video-quality picker, closing the long-standing ask in #852 and superseding #492 and #867:

ChewieController(
  videoPlayerController: controller,
  videoQualities: const [
    VideoQuality(id: '480', label: '480p'),
    VideoQuality(id: '1080', label: '1080p'),
  ],
  activeVideoQualityId: '1080',
  onVideoQualityChanged: (quality) {
    chewieController.swapVideoSource(
      VideoPlayerController.networkUrl(urlFor(quality)),
    );
  },
);

• VideoQuality {id, label} — id is opaque to chewie (a URL, an HLS rendition index, …).
• A Quality entry in the options menu of all three skins — Material, Material desktop, and Cupertino — with a selection dialog marking the active quality. Hidden until more than one quality is supplied (hasVideoQualities).
• setVideoQualities(...) for qualities known only after a manifest parses; selectVideoQuality(...) for programmatic selection; all three fields carried through copyWith.
• OptionsTranslation.qualityButtonText for i18n.

Design: why not a Map<String, String> of label → URL?

That's the shape #492 and #867 used, and it's the reason both stalled: it can't express HLS/DASH rendition switching (one URL, many qualities), per-quality headers or DRM, or qualities discovered after load — and it forces chewie to own controller recreation, the exact concern raised in the #867 review. Instead, chewie owns the UI and selection state, and the host owns the switch — for the common separate-files case that's the three-line swapVideoSource call from #963 shown above (demoed in the example app). This mirrors the shape of the subtitle/audio track proposals in #948/#949, so the three "pick one variant" features stay one pattern.

Thanks @akmalova (#867) and @merdweebner (#492) for the groundwork.

Tests

Unit tests for the controller surface (gating, set/select semantics, notifications, copyWith) and Material widget tests: menu gating, active-quality check mark, host callback on selection, and the qualityButtonText override.

[codecov]

Codecov Report

❌ Patch coverage is 98.21429% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.70%. Comparing base (7fb5885) to head (00d4b3a).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/src/cupertino/cupertino_controls.dart	97.36%	1 Missing ⚠️
lib/src/material/material_controls.dart	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #965      +/-   ##
==========================================
+ Coverage   72.73%   77.70%   +4.97%     
==========================================
  Files          41       43       +2     
  Lines        2560     2687     +127     
==========================================
+ Hits         1862     2088     +226     
+ Misses        698      599      -99     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[diegotori]

@Ortes looks like you have conflicts. Please resolve them. Thanks.

[diegotori]

LGTM.