Some wallet calls (like getbalances) need to lock the chainstate to make sure they are caught up on the latest block (which may have been reported to the users in getblockchaininfo or similar).

Those calls could benefit if the block hash they were valid on was included in the response. For example, immature balance can only change when the chainstate changes. (Assuming no keys are imported)

It seems those calls can include the block hash they are caught up with for free in the response. They could simply include `m_last_block_processed` in the response.

I haven't checked back with other developers to see if they like this approach, but to start simple only a single call could be updated for now. E.g. `getbalances`.

#### Useful skills:

Basic understanding of threads, the Bitcoin Core wallet and the Bitcoin Core RPC interface.

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{"passphrase", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "Encrypt the wallet with this passphrase."},
            {"avoid_reuse", RPCArg::Type::BOOL, RPCArg::Default{false}, "Keep track of coin reuse, and treat dirty and clean coins differently with privacy considerations in mind."},
            {"descriptors", RPCArg::Type::BOOL, RPCArg::Default{true}, "Create a native descriptor wallet. The wallet will use descriptors internally to handle address creation."
                                                                       " Setting to \"false\" will create a legacy wallet; however, the legacy wallet type is being deprecated and"
                                                                       " support for creating and opening legacy wallets will be removed in the future."},
            {"load_on_startup", RPCArg::Type::BOOL, RPCArg::Optional::OMITTED, "Save wallet name to persistent settings and load on startup. True to add wallet to startup list, false to remove, null to leave unchanged."},
            {"external_signer", RPCArg::Type::BOOL, RPCArg::Default{false}, "Use an external signer such as a hardware wallet. Requires -signer to be configured. Wallet creation will fail if keys cannot be fetched. Requires disable_private_keys and descriptors set to true."},
        },
        RPCResult{
            RPCResult::Type::OBJ, "", "",
            {
                {RPCResult::Type::STR, "name", "The wallet name if created successfully. If the wallet was created using a full path, the wallet_name will be the full path."},
                {RPCResult::Type::STR, "warning", true, "Warning messages, if any, related to creating the wallet. Multiple messages will be delimited by newlines. (DEPRECATED, returned only if config option -deprecatedrpc=walletwarningfield is passed.)"},
                {RPCResult::Type::ARR, "warnings", true, "Warning messages, if any, related to creating the wallet.",
                {
                    {RPCResult::Type::STR, "", ""},
                }},
            }
        },
        RPCExamples{
            HelpExampleCli("createwallet", "\"testwallet\"")
            + HelpExampleRpc("createwallet", "\"testwallet\"")
            + HelpExampleCliNamed("createwallet", {{"wallet_name", "descriptors"}, {"avoid_reuse", true}, {"descriptors", true}, {"load_on_startup", true}})
            + HelpExampleRpcNamed("createwallet", {{"wallet_name", "descriptors"}, {"avoid_reuse", true}, {"descriptors", true}, {"load_on_startup", true}})
        },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    WalletContext& context = EnsureWalletContext(request.context);
    uint64_t flags = 0;
    if (!request.params[1].isNull() && request.params[1].get_bool()) {