This is a fix for stellar/rs-soroban-sdk#1141, the basic problem described stellar/rs-soroban-sdk#1140 (comment)

If Arbitrary::arbitrary receives bytes it can't use it may return Error::IncorrectFormat. At present, if this happens the proptest will fail.

This patch uses the reject_local mechanism on the proptest test runner to reject these cases and try again. reject_local will eventually return an error if too many cases are rejected.

(I think we can probably do something similar for the random bytes buffer size, automatically increasing the buffer if Arbitrary returns NotEnoughData, but I have not done that yet).