bench: add on-disk HaveInputs benchmark

`CCoinsViewCache::HaveInputs()` is used by `Consensus::CheckTxInputs()` and currently exercises the `HaveCoin()` path in the UTXO cache.
Performance could be affected due to `Coin` copying and different cache warming behavior.

Add a benchmark to track `HaveInputs()` throughput before and after the `HaveCoin()` changes in this series to make sure the performance is retained.
The benchmark populates an on-disk `CCoinsViewDB` with dummy unspent coins for all block inputs and then calls `HaveInputs()` for each non-coinbase transaction using a fresh `CCoinsViewCache` (to avoid cross-iteration caching).
It calls `HaveInputs()` twice to exercise the cache-hit path as well.

Benchmark baseline:
|               ns/tx |                tx/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|            1,004.58 |          995,437.07 |    0.7% |      1.10 | `HaveInputsOnDisk`

src/bench/CMakeLists.txt

@@ -19,6 +19,7 @@ add_executable(bench_bitcoin
   checkblockindex.cpp
   checkqueue.cpp
   cluster_linearize.cpp
+  coins_haveinputs.cpp
   connectblock.cpp
   crypto_hash.cpp
   descriptors.cpp

src/bench/coins_haveinputs.cpp

@@ -0,0 +1,48 @@
+// Copyright (c) 2026-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://opensource.org/license/mit/.
+
+#include <bench/bench.h>
+#include <bench/data/block413567.raw.h>
+#include <coins.h>
+#include <consensus/amount.h>
+#include <primitives/block.h>
+#include <script/script.h>
+#include <streams.h>
+#include <test/util/setup_common.h>
+#include <txdb.h>
+#include <util/fs.h>
+
+#include <cassert>
+#include <ranges>
+
+static void HaveInputsOnDisk(benchmark::Bench& bench)
+{
+    const auto testing_setup{MakeNoLogFileContext<const BasicTestingSetup>(ChainType::REGTEST)};
+    const auto path{testing_setup->m_path_root / fs::PathFromString(bench.name())};
+    CCoinsViewDB db{{.path = path, .cache_bytes = 1_MiB, .memory_only = false, .wipe_data = true}, {}};
+
+    CBlock block;
+    DataStream{benchmark::data::block413567} >> TX_WITH_WITNESS(block);
+    const uint256 best_block{block.GetHash()};
+
+    CCoinsViewCache cache{&db};
+    cache.SetBestBlock(best_block);
+    for (auto& tx : block.vtx | std::views::drop(1)) {
+        for (auto& txin : tx->vin) {
+            cache.AddCoin(txin.prevout, {{COIN, CScript()}, /*nHeightIn=*/1, /*fCoinBaseIn=*/false}, /*possible_overwrite=*/false);
+        }
+    }
+    cache.Flush();
+
+    bench.batch(block.vtx.size() - 1).unit("tx").run([&] {
+        CCoinsViewCache view{&db}; // Recreate to avoid caching
+        view.SetBestBlock(best_block);
+        for (auto& tx : block.vtx | std::views::drop(1)) {
+            assert(view.HaveInputs(*tx));
+            assert(view.HaveInputs(*tx)); // Exercise the cache-hit path as well.
+        }
+    });
+}
+
+BENCHMARK(HaveInputsOnDisk);