Add TimeLimitSnapshotTrait helpers for seconds?

Currently it's limited to minutes just like the Swift Testing seems to be.

It seems odd that Swift Testing only has TimeLimitTrait.Duration helper for .minutes

Maybe our helper should use the standard library's Duration type and convert on the fly to Swift Testing's `minutes`

Start by locating the TimeLimitSnapshotTrait helpers and the Swift Testing TimeLimitTrait.Duration usage mentioned in the issue. Compare the supported minute-based API with Swift’s standard Duration type, then verify that the helper can accept seconds and still convert correctly to Swift Testing’s minutes representation.

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