refactor: Reserve vectors in fuzz tests

* Since the main LIMITED_WHILE stated `outpoints.size() < 200'000`, I've presized outpoints accordingly.
* `tx_mut.vin` and `tx_mut.vout` weren't caught by the clang-tidy, but addressed them anyway.

Author: l0rinc

src/test/fuzz/txorphan.cpp

@@ -38,6 +38,7 @@ FUZZ_TARGET(txorphan, .init = initialize_orphanage)
 
     TxOrphanage orphanage;
     std::vector<COutPoint> outpoints; // Duplicates are tolerated
+    outpoints.reserve(200'000);
 
     // initial outpoints used to construct transactions later
     for (uint8_t i = 0; i < 4; i++) {
@@ -55,12 +56,14 @@ FUZZ_TARGET(txorphan, .init = initialize_orphanage)
             const auto num_out = fuzzed_data_provider.ConsumeIntegralInRange<uint32_t>(1, 256);
             // pick outpoints from outpoints as input. We allow input duplicates on purpose, given we are not
             // running any transaction validation logic before adding transactions to the orphanage
+            tx_mut.vin.reserve(num_in);
             for (uint32_t i = 0; i < num_in; i++) {
                 auto& prevout = PickValue(fuzzed_data_provider, outpoints);
                 // try making transactions unique by setting a random nSequence, but allow duplicate transactions if they happen
                 tx_mut.vin.emplace_back(prevout, CScript{}, fuzzed_data_provider.ConsumeIntegralInRange<uint32_t>(0, CTxIn::SEQUENCE_FINAL));
             }
             // output amount will not affect txorphanage
+            tx_mut.vout.reserve(num_out);
             for (uint32_t i = 0; i < num_out; i++) {
                 tx_mut.vout.emplace_back(CAmount{0}, CScript{});
             }

src/test/fuzz/util.h

@@ -79,6 +79,7 @@ template<typename B = uint8_t>
 {
     const size_t n_elements = fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, max_vector_size);
     std::vector<std::string> r;
+    r.reserve(n_elements);
     for (size_t i = 0; i < n_elements; ++i) {
         r.push_back(fuzzed_data_provider.ConsumeRandomLengthString(max_string_length));
     }
@@ -90,6 +91,7 @@ template <typename T>
 {
     const size_t n_elements = fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, max_vector_size);
     std::vector<T> r;
+    r.reserve(n_elements);
     for (size_t i = 0; i < n_elements; ++i) {
         r.push_back(fuzzed_data_provider.ConsumeIntegral<T>());
     }