fuzz: populate wallet TXO index in wallet_create_transaction #35790

A refactor in #27286 seemingly caused a regression in this harness. Rewiring to m_txos from mapWallet makes the setup loop in wallet_create_transaction, which uses raw mapWallet.emplace(), to no longer see coins. Therefore, GetTXO/GetTXOs probably return empty. To make coin selection possible, this fix calls RefreshTXOsFromTx after each insertion.

<details> <summary>Coverage diff on select functions</summary>

diff spend_cov_before.txt spend_cov_after.txt on src/wallet/spend.cpp:

-  748|      0|  if (auto bnb_result{SelectCoinsBnB(...)}) {
+  748|  2.14k|  if (auto bnb_result{SelectCoinsBnB(...)}) {

-  761|      0|  if (auto knapsack_result{KnapsackSolver(...)}) {
+  761|  4.46k|  if (auto knapsack_result{KnapsackSolver(...)}) {

-  766|      0|  if (auto cg_result{CoinGrinder(...)}) {
+  766|  2.88k|  if (auto cg_result{CoinGrinder(...)}) {

-  774|      0|  if (auto srd_result{SelectCoinsSRD(...)}) {
+  774|  4.46k|  if (auto srd_result{SelectCoinsSRD(...)}) {

-  845|      0|  auto op_selection_result = AutomaticCoinSelection(...);
+  845|  1.27k|  auto op_selection_result = AutomaticCoinSelection(...);

-  960|      0|  if (auto res{AttemptSelection(...)}) {
+  960|  1.36k|  if (auto res{AttemptSelection(...)}) {

- 1484|      0|  auto txr_grouped = CreateTransactionInternal(...);
+ 1484|    380|  auto txr_grouped = CreateTransactionInternal(...);

</details>

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35790.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #35716 (wallet: Replace mapWallet and wtxOrdered with a boost::multi_index by achow101)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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code review ACK 1eac6a728bfc3ea6a7b95be6db69cce87e0f046f

Nice catch! Perhaps in a follow-up we could track the number of inserted outputs and assert that the size of GetTXOs matches it, it would have gotten that.