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.
