feat: example improvements

[Gustl22]

Description

• add ability to change Android and iOS specific contexts
• Permission for WAKE_LOCK and MODIFY_AUDIO_SETTINGS
• improved layout of widgets (more spacing, responsive height, etc.)
• preserve state for each player
• style toggles
• add some icons

Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs:, chore: etc).
• I have read the Contributor Guide and followed the process outlined for submitting PRs.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation and added dartdoc comments with ///, where necessary.
• I have updated/added relevant examples in example.

Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

Related Issues

[Gustl22]

@spydon I now found a way to omit PlayerUiState which is much more elegant. And did some more small changes. Only noting, if you want to review again...

[spydon]

Not sure why the checks are failing (haven't checked, I'm in the alps 😅)