[Version-unspecific] Instant observations (and their SetSigned) rather than delayed to the end of the processTransactions queue (after any failed transaction RemoveSigned)

[Version-unspecific]

This is intended to close #1837 (closed)
'Failed outbounds not properly removed from ethereum (and evm?) signer cache'
, but alternative or complementary approaches are also welcome.

My full reasoning is here:
#1837 (comment 1728126863)