Add -audioPlayer:didSeek:toFrame: delegate method

[sbooth]

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[Copilot]

Pull request overview

This PR adds a new SFBAudioPlayerDelegate callback to notify clients when a user-initiated seek has completed, including the decoder instance and the resulting frame position.

Changes:

• Introduces a new decoding event type (DecodingEventCommand::seek) and emits it after a successful seek.
• Adds decoding-event handling to invoke the new delegate selector -audioPlayer:didSeek:toFrame:.
• Extends the public SFBAudioPlayerDelegate protocol with the new optional method and updates delegate-notification documentation.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
Sources/CSFBAudioEngine/Player/AudioPlayer.mm	Emits and processes a new seek decoding event, dispatching the new delegate callback with the resulting frame.
Sources/CSFBAudioEngine/Player/AudioPlayer.h	Adds the seek decoding event command and declares processDecoderSeekEvent().
Sources/CSFBAudioEngine/include/SFBAudioEngine/SFBAudioPlayer.h	Adds the public optional delegate method -audioPlayer:didSeek:toFrame: and updates the delegate-notification list.

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