DA: Don't choose utxos on every nonce probe

[kpp]

Followup of #925:

#925 (comment):

since we decided to go with wtxid for prefixes, now we have to choose utxos every time we try a nonce.
this can be improved actually.

How?

We loop over nonceCalculate reveal addr Then build commit tx — which selects utxos

[eyusufatik]

the utxos chosen in the commit tx affect the commit txid

which affects reveal tx's txid and wtxid

but once a set of utxos are chosen, we don't need to re-select them.

one problem that may rise is taproot addresses don't have a fixed length and that might change the tx sizes? (I'm not completely sure about this)

[kpp]

I am not quite sure if it's a correct strategy. If fee increases while we are mining wtxid, we need to re-select utxos if their sum < fee.

[eyusufatik]

I am not quite sure if it's a correct strategy. If fee increases while we are mining wtxid, we need to re-select utxos if their sum < fee.

we don't requery fees while mining, but yes. we should actually at some intervals