[camera_avfoundation] Pigeon swift migration - part 1

[RobertOdrowaz]

Prepares camera package for pigeon Swift migration as part of flutter/flutter#119109

Current implementation of FormatUtils.selectBestFormat overrides MediaSettings.framesPerSecond. With swift pigeon contracts MediaSettings is non mutable so that will no longer be possible.

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[gemini-code-assist]

Code Review

This pull request effectively refactors the camera package to remove its dependency on the mutability of MediaSettings, which is a necessary preparation for the upcoming Pigeon Swift migration. The changes are well-contained and logical, primarily by introducing a local framesPerSecond property in DefaultCamera and making FormatUtils.findBestFormat a pure function. I have one minor suggestion to improve code readability.

[hellohuanlin]

could you explain more about what this means? Is it removing a feature?