Cancel a bridged .task(id:) when its id changes or the view leaves

[Ceylo]

What

In a Fuse app, a .task / .task(id:) is never cancelled when its id changes or its view leaves: the old Swift task runs to completion with Task.isCancelled == false. This PR cancels it in both cases, as on iOS.

Since #420, task(id:bridgedAction:) runs in a SkipLib Task and waits on invokeOnCancellation. But SkipLib's Task.cancel() never cancels the coroutine; it only runs handlers registered with withTaskCancellationHandler. So the action's onCancel was never called.

The fix calls the action, then waits for its completion under withTaskCancellationHandler. Registering after the action has installed onCancel also covers a cancel that lands while the action is still starting: SkipLib then calls the handler at once. Either way it runs once. The task also now calls the action it was created with, rather than reading it through rememberUpdatedState when its coroutine starts.

Pull-to-refresh is not affected: List and ScrollView launch RefreshAction in a Compose scope, whose cancellation is real. A test pins that down.

Before / after

Three new Robolectric tests fail on main and pass here. Each also checks that onCancel runs once.

test	fails on main with
testBridgedTaskCancelledWhenIdChanges	The task for the previous id was not cancelled
testBridgedTaskCancelledWhenViewLeaves	The task of the removed view was not cancelled
testBridgedTaskCancelledBeforeItsActionInstallsOnCancel	The task cancelled before its action installed onCancel was not cancelled

Showcase in Fuse, with temporary log lines in two playgrounds:

	before	after
Timer: open, then Back	kept ticking, never ended	ended 1.1 s after Back
Sensors: Start, then Stop	240 more events in 11 s, never ended	ended within 3.8 s, 3 of 3 times

Side effects

• Every bridged .task in a Fuse app is now cancelled when its view leaves, as on iOS. Code relying on a task outliving its view relied on this bug.
• Not covered: RefreshAction.run(completion:) and the Lite task(id:priority:) overload are unchanged.
• Alternative, if you prefer: the bridged overload could go back to LaunchedEffect without the crash Cancel .task task on dispose, instead of crashing the app #420 fixed. I kept Cancel .task task on dispose, instead of crashing the app #420's Task model.

Verified

• swift test: 120 Swift tests, 57 skipped, 0 failures. JUnit: 164 tests, 159 passed, 5 skipped.
• Mutation runs: with main's file each new test fails as above; with the handler registered before the action, only the third fails.
• Showcase built through Gradle against this branch, run in Fuse on an API 37 emulator before and after. Lite doesn't use this path. Not run on iOS: the change is Kotlin-only.

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Skip Pull Request Checklist:

• REQUIRED: I have signed the Contributor Agreement
• REQUIRED: I have tested my change locally with swift test
• OPTIONAL: I have tested my change on an iOS simulator or device. Not run: the change is Kotlin-only.
• OPTIONAL: I have tested my change on an Android emulator or device
• REQUIRED: I have checked whether this change requires a corresponding update in the Skip Fuse UI repository (link related PR if applicable). No API change, so no paired PR.
• OPTIONAL: I have added an example of any UI changes to the Showcase sample app. No visible change.

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Written with Claude Code: the fix, the tests and this description. Every claim above comes from a run: swift test, the mutation runs, and the Showcase in Fuse on an emulator before and after.