- update to use `bitcoin::Amount` on `CreateTxError::FeeTooLow` variant.
- update to use `bitcoin::Amount` on `Wallet::calculate_fee()`.
- update to use `bitcoin::Amount` on `FeePolicy::fee_absolute()`.
- update to use `bitcoin::SignedAmount` on
`CalculateFeeError::NegativeFee` variant.
- update to use `bitcoin::Amount` on `TxGraph::calculate_fee()`.
- update to use `bitcoin::Amount` on `PsbUtils::fee_amount()`