fix: Resolve Media3 binary compatibility crashes in DownloadHelper callbacks

[syed-tp]

• Media3 has been upgraded to 1.8.0 to fix runtime AbstractMethodError
  crashes encountered by client apps.
• This implements the mandatory boolean parameter in the onPrepared signature required by newer versions,
  ensuring the player works across all current Media3 environments.

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[gemini-code-assist]

Code Review

This pull request updates the media3 library version from 1.7.1 to 1.8.0 and adjusts the DownloadHelper.Callback implementation in DownloadController.kt to include the new helperPrepared parameter. Feedback was provided to ensure that the helperPrepared flag is checked before interacting with the helper object, as failing to do so could result in an IllegalStateException if the helper was released during preparation.