[video_player_avplay] Fix the issue where seeking the beginning of the live DASH manifest fails.

[gin7773]

Main changes:

• Update plusplayer
  1. [DASH] Fix the issue where seeking the beginning of the live DASH manifest fails.

[gemini-code-assist]

Code Review

This pull request increments the package version to 0.8.6 in pubspec.yaml, README.md, and CHANGELOG.md. The changelog is updated to reflect the fix for an issue where seeking to the beginning of a live DASH manifest would fail. I have provided one suggestion to improve the formatting of the changelog entry for better clarity and conciseness.

[JSUYA]

Hi @gin7773 @xiaowei-guan

There is currently a network issue on the integration test host PC. The test requires cloning https://github.com/flutter/packages.git for flutter_plugin_tools, but a 403 error is occurring only for packages.git.
https://github.com/flutter-tizen/plugins/actions/runs/23417947039

We are currently investigating the cause.
I have manually published this PR.
https://pub.dev/packages/video_player_avplay

Please always make sure to verify that the release CI is functioning correctly after merging the PR into master.
If any problems arise, please let me know.

+) @seungsoo47