Mark unrecoverable payjoin sessions in storage so they don't spawn

[DanGould]

We mark successful payjoins so that they don't spawn more isolates (#400)

A similar approach will prevent so many isolates for spawning in the case of

• Unrecoverable errors
• Expired payjoins

However, error handling in payjoin-flutter and even to some extent rust-payjoin is incomplete.

I can start with a broad brush and mark entire error variants produced by payjoin-flutter as unrecoverable in storage, knowing that the underlying library will change as our error propagation becomes more robust. This is acknowledged tech debt. I'm going to try to balance fixing the problem in the short term without complete engineering, because I know it's going to need to change as soon as the library updates.