fix: parse rid and ssrc to proper types

[Yash-Garg]

This caused an issue on Safari where tracks were not being published properly due to rid being 0 and getting parsed as an int rather than a String.

Tested on Safari, Chrome & Firefox.

[Error] TypeError: 0: type 'int' is not a subtype of type 'String?'
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package:livekit_client/src/widgets/video_track_renderer.dart.js 10532:72      LocalVideoTrackExt$124setDegradationPreference
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dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 647:23           <fn>
dart-sdk/lib/async/future_impl.dart 951:44                                    handleValueCallback
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dart-sdk/lib/async/future_impl.dart 723:5                                     <fn>
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dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 186:15           <fn>