Consider unconfirmed ancestors in tx fee estimation

[notmandatory]

"You consider unconfirmed coins when creating a transaction, but you do not account for the size of their ancestors. This can lead to largely underestimating the fees for the transaction, and to reporting a largely overestimated feerate to the user."

[oleonardolima]

I'll take a look at this one.

[aagbotemi]

@oleonardolima are you still actively working on this? If not, I'd like to take it on. I have an implementation approach mapped out across
bdk_coin_select, bdk_chain, bdk_tx, and bdk_wallet, motivated by the
discussion in #370 (comment).

[oleonardolima]

@oleonardolima are you still actively working on this? If not, I'd like to take it on. I have an implementation approach mapped out across bdk_coin_select, bdk_chain, bdk_tx, and bdk_wallet, motivated by the discussion in #370 (comment).

No, feel free to work on it.