Fix(web): Keep playback when entering/exiting fullscreen on web

[victorspringer]

Adresses issue #846

Description

• Problem: On Flutter Web, entering or exiting fullscreen can stall playback or force a pause; users often need to manually pause -> play to recover.
• Root cause: The platform view rebuild during fullscreen disrupts the HTML video element’s stream/state.

Solution

• Enter fullscreen (web-only): After the first fullscreen frame, force a quick pause -> 10ms delay -> play if the video was previously playing; if it was paused, briefly play then pause to prime a frame.
• Exit fullscreen (web-only): Re-initialize the VideoPlayerController, seek back to the previous position, and restore the prior play/pause state.
• All changes are guarded by kIsWeb; non-web platforms are unaffected.

[diegotori]

LGTM.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.03%. Comparing base (d51d4e5) to head (6ceb832).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/src/chewie_player.dart	0.00%	23 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #927      +/-   ##
==========================================
- Coverage   44.47%   44.03%   -0.45%     
==========================================
  Files          21       21              
  Lines        1585     1601      +16     
==========================================
  Hits          705      705              
- Misses        880      896      +16     

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