chore: move to spark review follow-ups #1802

Refs: #1774

Low-severity items from the reviews of #1774 that it leaves out:

• Tests: MoveToSparkRepo.move() (event matching, the in-flight timeout, the fee cap passed to payInvoiceOverLdk) and the state transitions of MoveToSparkViewModel have no unit tests.
• Outcome after Back: leaving the Move to Spark screen while a move runs cancels the screen's wait, since MoveToSparkViewModel is tied to the screen. The payment still goes through, but a successful move then gives no feedback, because the move's notices are muted. Keep the outcome after the screen closes, as iOS's shared MoveToSparkManager does, or block Back while the move runs (QA review).
• Restart: MoveToSparkRepo keeps the move's payment hashes in memory only. If the app is killed while the payment is in flight and Spark reports the receive after relaunch, the usual received notice shows. Keep the hash until the payment settles (QA review).