fuzz: add util/mempool/h.cpp

Moving the mempool code (Boost) out of util.h, results in a ~10% speedup
(for me) when compiling the fuzz tests.

src/test/fuzz/util/mempool.cpp

@@ -0,0 +1,27 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <consensus/amount.h>
+#include <primitives/transaction.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/util.h>
+#include <test/fuzz/util/mempool.h>
+#include <txmempool.h>
+
+#include <limits>
+
+CTxMemPoolEntry ConsumeTxMemPoolEntry(FuzzedDataProvider& fuzzed_data_provider, const CTransaction& tx) noexcept
+{
+    // Avoid:
+    // policy/feerate.cpp:28:34: runtime error: signed integer overflow: 34873208148477500 * 1000 cannot be represented in type 'long'
+    //
+    // Reproduce using CFeeRate(348732081484775, 10).GetFeePerK()
+    const CAmount fee = std::min<CAmount>(ConsumeMoney(fuzzed_data_provider), std::numeric_limits<CAmount>::max() / static_cast<CAmount>(100000));
+    assert(MoneyRange(fee));
+    const int64_t time = fuzzed_data_provider.ConsumeIntegral<int64_t>();
+    const unsigned int entry_height = fuzzed_data_provider.ConsumeIntegral<unsigned int>();
+    const bool spends_coinbase = fuzzed_data_provider.ConsumeBool();
+    const unsigned int sig_op_cost = fuzzed_data_provider.ConsumeIntegralInRange<unsigned int>(0, MAX_BLOCK_SIGOPS_COST);
+    return CTxMemPoolEntry{MakeTransactionRef(tx), fee, time, entry_height, spends_coinbase, sig_op_cost, {}};
+}

src/test/fuzz/util/mempool.h

@@ -0,0 +1,24 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_TEST_FUZZ_UTIL_MEMPOOL_H
+#define BITCOIN_TEST_FUZZ_UTIL_MEMPOOL_H
+
+#include <primitives/transaction.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <txmempool.h>
+#include <validation.h>
+
+class DummyChainState final : public Chainstate
+{
+public:
+    void SetMempool(CTxMemPool* mempool)
+    {
+        m_mempool = mempool;
+    }
+};
+
+[[nodiscard]] CTxMemPoolEntry ConsumeTxMemPoolEntry(FuzzedDataProvider& fuzzed_data_provider, const CTransaction& tx) noexcept;
+
+#endif // BITCOIN_TEST_FUZZ_UTIL_MEMPOOL_H