[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.

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

Note: The Flutter team is currently trialing the use of Gemini Code Assist for GitHub. Comments from the gemini-code-assist bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩↩²↩³

[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.