Implement new RBF logic for cluster mempool

With a total ordering on mempool transactions, we are now able to calculate a
transaction's mining score at all times. Use this to improve the RBF logic:

- we no longer enforce a "no new unconfirmed parents" rule

- we now require that the mempool's feerate diagram must improve in order
  to accept a replacement

- the topology restrictions for conflicts in the package rbf setting have been
  eliminated

Revert the temporary change to mempool_ephemeral_dust.py that were previously
made due to RBF validation checks being reordered.

Co-authored-by: Gregory Sanders <gsanders87@gmail.com>, glozow <gloriajzhao@gmail.com>

src/test/fuzz/rbf.cpp

@@ -144,9 +144,7 @@ FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
         }
         assert(!pool.GetIter(parent_entry.GetTx().GetHash()));
         AddToMempool(pool, parent_entry);
-        if (fuzzed_data_provider.ConsumeBool()) {
-            child.vin[0].prevout = COutPoint{mempool_txs.back().GetHash(), 0};
-        }
+        child.vin[0].prevout = COutPoint{mempool_txs.back().GetHash(), 0};
         mempool_txs.emplace_back(child);
         const auto child_entry = ConsumeTxMemPoolEntry(fuzzed_data_provider, mempool_txs.back());
         running_vsize_total += child_entry.GetTxSize();