[camera_avfoundation] Wrappers swift migration - part 4

[RobertOdrowaz]

Migrates camera wrappers as part of flutter/flutter#119109

This PR migrates wrappers to Swift:

• FLTCaptureConnection
• FLTCaptureDeviceFormat
• FLTAssetWriter

In line with Swift conventions, the FLT prefixes are removed. The Default class implementations are replaced with protocol conformance on base AV classes.

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.

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Footnotes

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[gemini-code-assist]

Code Review

This pull request continues the migration of Objective-C code to Swift by converting FLTCaptureConnection, FLTCaptureDeviceFormat, and FLTAssetWriter from wrapper classes to Swift protocols. This is a solid architectural improvement that makes the code more idiomatic and type-safe. The changes are consistently applied throughout the codebase, including tests and mocks. I have one minor suggestion to further align the code with Swift conventions.

[gemini-code-assist]

The return type (any CaptureConnection)? can be simplified to CaptureConnection?. The any keyword is only required for protocols with Self or associated type requirements when used as a type, which is not the case for CaptureConnection. This change makes the signature more idiomatic.

Suggested change

	func connection(with mediaType: AVMediaType) -> (any CaptureConnection)? {
	func connection(with mediaType: AVMediaType) -> CaptureConnection? {