Optimizes coin selection by performing the "group outputs"
procedure only once, outside the "attempt selection" process.
Avoiding the repeated execution of the 'GroupOutputs' operation
that occurs on each coin eligibility filters (up to 8 of them);
then for every coin vector type plus one for all the coins together.
This also let us not perform coin selection over coin eligibility
filtered groups that don't add new elements.
(because, if the previous round failed, and the subsequent one has
the same coins, then this new round will fail again).
The 'GroupOutputs()' function performs the same
calculations for only-positive and mixed groups,
the only difference is that when we look for
only-positive groups, we discard negative utxos.
So, instead of wasting resources calling GroupOutputs()
for positive-only first, then call it again to include
the negative ones in the result, we can execute
GroupOutputs() only once, including in the response
both group types (positive-only and mixed).
The following scenarios are covered:
1) 10 UTXO with the same script:
partial spends is enabled --> outputs must not be grouped.
2) 10 UTXO with the same script:
partial spends disabled --> outputs must be grouped.
3) 20 UTXO, 10 one from scriptA + 10 from scriptB:
a) if partial spends is enabled --> outputs must not be grouped.
b) if partial spends is not enabled --> 2 output groups expected (one per script).
3) Try to add a negative output (value - fee < 0):
a) if "positive_only" is enabled --> negative output must be skipped.
b) if "positive_only" is disabled --> negative output must be added.
4) Try to add a non-eligible UTXO (due not fulfilling the min depth target for
"not mine" UTXOs) --> it must not be added to any group
5) Try to add a non-eligible UTXO (due not fulfilling the min depth target for
"mine" UTXOs) --> it must not be added to any group
6) Surpass the 'OUTPUT_GROUP_MAX_ENTRIES' size and verify that a second partial
group gets created.
