[Bitcoin]: UTXO selection and dust improvements

[satoshiotomakan]

Description

• Add SigningInput::Proto::dust_policy with the fixed_dust_threshold option.
• Filter out Dust UTXOs before actual UTXO selecting.
• Do not include change output if it's "dust".
• Validate the requested amount if it's "dust".
• InputSelector::select returns entire list of UTXOs if it couldn't find a combination of inputs to cover estimated transaction fee and the target amount. This is needed, because FeeEstimator estimates Segwit transaction too rough, however later, in estimateSegwitFee function, the transaction fee is significantly less, so the given UTXOs enough to cover it.

How to test

Run C++ tests

Types of changes

Checklist

• Create pull request as draft initially, unless its complete.
• Add tests to cover changes as needed.
• Update documentation as needed.
• If there is a related Issue, mention it in the description.

If you're adding a new blockchain

• I have read the guidelines for adding a new blockchain.

[lamafab]

So disclaimer - I don't grasp the full C++ implementation, but generally this LGTM.

[lamafab]

Generally speaking, is it even appropriate to refer to this as dustAmount?

int64_t LinearFeeCalculator::calculateSingleInput(int64_t byteFee) const noexcept {
    return static_cast<int64_t>(std::ceil(bytesPerInput)) * byteFee; // std::ceil(101.25) = 102
}

[satoshiotomakan]

No, but this is how our current chains work. This is a tradeoff to avoid breaking changes for other Bitcoin forks.