Calculate cost_of_change

Instead of passing the cost_of_change param, calculate the cost of
creating a change output using InputWeightPrediction.

benches/coin_selection.rs

@@ -5,13 +5,12 @@ use bitcoin::FeeRate;
 use bitcoin::ScriptBuf;
 use bitcoin::TxOut;
 use bitcoin::Weight;
+
+use bitcoin::transaction::InputWeightPrediction;
 use rust_bitcoin_coin_selection::select_coins_bnb;
 use rust_bitcoin_coin_selection::WeightedUtxo;
 
 pub fn criterion_benchmark(c: &mut Criterion) {
-    // https://github.com/bitcoin/bitcoin/blob/f3bc1a72825fe2b51f4bc20e004cef464f05b965/src/wallet/coinselection.h#L18
-    let cost_of_change = Amount::from_sat(50_000);
-
     let one = WeightedUtxo {
         satisfaction_weight: Weight::ZERO,
         utxo: TxOut { value: Amount::from_sat(1_000), script_pubkey: ScriptBuf::new() },
@@ -30,7 +29,7 @@ pub fn criterion_benchmark(c: &mut Criterion) {
         b.iter(|| {
             let result: Vec<_> = select_coins_bnb(
                 black_box(target),
-                black_box(cost_of_change),
+                black_box(InputWeightPrediction::P2WPKH_MAX),
                 black_box(FeeRate::ZERO),
                 black_box(FeeRate::ZERO),
                 black_box(&utxo_pool),