Close saved-payment-method confirmation interactors when they leave composition

[jaynewstrom-stripe]

Summary

SavedPaymentMethodConfirmInteractor now exposes close(), which cancels its internal selection-collecting job. PaymentSheetScreen.SavedPaymentMethodConfirm implements Closeable and delegates to it. In the embedded form, FormScreenContent now remembers the interactor keyed on the selection being confirmed and closes it via DisposableEffect when it leaves composition or the selection changes.

Motivation

DefaultSavedPaymentMethodConfirmInteractor launched a coroutineScope.launch { selection.collectLatest { updateSelection(it) } } job in init with no way to stop it — every time the saved-payment confirmation screen/composable was shown, that collector leaked for the life of the underlying scope. This adds an explicit disposal hook and wires it up at both places the interactor is created: the standalone PaymentSheetScreen.SavedPaymentMethodConfirm screen and the embedded FormActivityUI's FormScreenContent composable.

Testing

• Added tests

• Modified tests

• Manually verified

• Added a DefaultSavedPaymentMethodConfirmInteractorTest case verifying that after close(), selection updates stop being delivered. Wired a CleanupTestRule so every interactor built by the test helper gets closed during test cleanup.

• Added FormScreenContentTest covering the remember/DisposableEffect semantics in the embedded form: the interactor is reused across unrelated recompositions of the same selection, closed exactly once when the confirmation is dismissed, and recreated (with the old one closed) when the selection changes.

• Added a PaymentSheetScreen test verifying SavedPaymentMethodConfirm.close() delegates to the interactor's close().

• FakeSavedPaymentMethodConfirmInteractor got a no-op close() to satisfy the interface.

Screenshots

N/A — no visual changes.