Swift testing support for attachments

[tahirmt]

Describe the bug
Currently swift testing failures don't include attachments. It was introduced in Swift 6.2 https://github.com/swiftlang/swift-evolution/blob/main/proposals/testing/0009-attachments.md

To Reproduce
Have any snapshot failures in swift testing. The steps are irrelevant.

Expected behavior
There should be attachments on the failures with failure and reference images.

Environment

• swift-snapshot-testing version [e.g. 1.18.7]
• Xcode [e.g. 26.2]
• Swift [e.g. 6.2]
• OS: [e.g. iOS 26]

Additional context
I know it's new and probably not implemented yet but hoping for a ticket to track it.

[adammcarter]

There's a discussion here: #909