[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)

bifrost/signer/sign.go

@@ -209,22 +209,7 @@ func (s *Signer) processTransactions() {
 		go func(items []TxOutStoreItem) {
 			chain := items[0].TxOutItem.Chain // all items in a batch should be the same chain
 
-			// make all observations for the batch before returning
-			observations := []types.TxInItem{}
 			defer func() {
-				if len(observations) > 0 {
-					s.observer.ObserveSigned(types.TxIn{
-						Count:                strconv.Itoa(len(observations)),
-						Chain:                chain,
-						TxArray:              observations,
-						MemPool:              true,
-						Filtered:             true,
-						SentUnFinalised:      false,
-						Finalised:            false,
-						ConfirmationRequired: 0,
-					}, chain.IsEVM()) // Instant EVM observations have wrong gas and need future correct observations
-				}
-
 				wg.Done()
 			}()
 
@@ -293,9 +278,19 @@ func (s *Signer) processTransactions() {
 					}
 					cancel()
 
-					// if enabled and the observation is non-nil, add to this batch's observations
+					// if enabled and the observation is non-nil, instant-observe without waiting for end of batch's range
+					// (aim to instant-observe SetSigned prior to any failed transaction RemoveSigned)
 					if s.cfg.AutoObserve && obs != nil {
-						observations = append(observations, *obs)
+						s.observer.ObserveSigned(types.TxIn{
+							Count:                "1",
+							Chain:                chain,
+							TxArray:              []types.TxInItem{*obs},
+							MemPool:              true,
+							Filtered:             true,
+							SentUnFinalised:      false,
+							Finalised:            false,
+							ConfirmationRequired: 0,
+						}, chain.IsEVM()) // Instant EVM observations have wrong gas and need future correct observations
 					}
 
 					// We have a successful broadcast! Remove the item from our store