fix: Prevent PlayerController init on unsupported platforms

[Namaneo]

Description

The audio_waveforms package only supports Android and iOS, and playerController.dispose() was called unconditionally, which cause an exception to be raised on unsupported platforms whenever the chat view is disposed. This PR fixes this issue by only initializing a PlayerController when actually supported.

Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs: etc).
• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

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

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