Merge bitcoin/bitcoin#27846: [coinselection] Increase SRD target by change_fee

1771daa815 [fuzz] Show that SRD budgets for non-dust change (Murch)
941b8c6539 [bug] Increase SRD target by change_fee (Murch)

Pull request description:

  I discovered via fuzzing of another coin selection approach that at extremely high feerates SRD may find input sets that lead to transactions without change outputs. This is an unintended outcome since SRD is meant to always produce a transaction with a change output—we use other algorithms to specifically search for changeless solutions.

  The issue occurs when the flat allowance of 50,000 ṩ for change is insufficient to pay for the creation of a change output with a non-dust amount, at and above 1,613 ṩ/vB. Increasing the change budget by `change_fee` makes SRD behave as expected at any feerates.

  Note: The intermittent failures of `test/functional/interface_usdt_mempool.py` are a known issue: https://github.com/bitcoin/bitcoin/issues/27380

ACKs for top commit:
  achow101:
    ACK 1771daa815
  S3RK:
    ACK 1771daa815

Tree-SHA512: 3f36a3e317ef0a711d0e409069c05032bff1d45403023f3728bf73dfd55ddd9e0dc2a9969d4d69fe0a426807ebb0bed1f54abfc05581409bfe42c327acf766d4

src/wallet/test/coinselector_tests.cpp

@@ -968,7 +968,7 @@ static util::Result<SelectionResult> SelectCoinsSRD(const CAmount& target,
     std::unique_ptr<CWallet> wallet = NewWallet(m_node);
     CoinEligibilityFilter filter(0, 0, 0); // accept all coins without ancestors
     Groups group = GroupOutputs(*wallet, coin_setup(*wallet), cs_params, {{filter}})[filter].all_groups;
-    return SelectCoinsSRD(group.positive_group, target, cs_params.rng_fast, max_weight);
+    return SelectCoinsSRD(group.positive_group, target, cs_params.m_change_fee, cs_params.rng_fast, max_weight);
 }
 
 BOOST_AUTO_TEST_CASE(srd_tests)