The `getaddressesbylabel` API spends a lot more time than the `getaddressesbyaccount` API.

I generated addresses by the `getnewaddress` API, then, I measured time that the `getaddressesby*` API spends. It seems the algorithm of the `getaddressesbylabel` API takes **O(N ^ 2)** time! The results of my survey are as follows.

### getaddressesbylabel

bitcoind v0.17.1 on Ubuntu 16.04 (AWS EC2 t3.large)

#### 11,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbylabel ""
# (omitted)
real    0m1.230s # 1.2s
user    0m0.044s
sys 0m0.048s
```

#### 111,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbylabel ""
# (omitted)
real    1m37.027s # 97.0s
user    0m0.408s
sys 0m0.544s
```

#### 211,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbylabel ""
# (omitted)
real    6m3.727s # 363.7s
user    0m0.800s
sys 0m0.900s
```

### getaddressesbyaccount

bitcoind v0.16.3 on Ubuntu 16.04 (AWS EC2 t3.large)

#### 11,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbyaccount ""
# (omitted)
real    0m0.500s # 0.5s
user    0m0.092s
sys 0m0.160s
```

#### 111,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbyaccount ""
# (omitted)
real    0m1.361s # 1.4s
user    0m0.168s
sys 0m0.348s
```

#### 211,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbyaccount ""
# (omitted)
real    0m2.220s # 2.2s
user    0m0.384s
sys 0m0.532s
```

if (request.fHelp || request.params.size() != 0)
        throw std::runtime_error(
            RPCHelpMan{"resendwallettransactions",
                "Immediately re-broadcast unconfirmed wallet transactions to all peers.\n"
                "Intended only for testing; the wallet code periodically re-broadcasts\n"
                "automatically.\n",
                {},
                RPCResult{
            "Returns an RPC error if -walletbroadcast is set to false.\n"
            "Returns array of transaction ids that were re-broadcast.\n"
                },
                 RPCExamples{""},
             }.ToString()
            );
    if (!g_connman)
        throw JSONRPCError(RPC_CLIENT_P2P_DISABLED, "Error: Peer-to-peer functionality missing or disabled");
    auto locked_chain = pwallet->chain().lock();
    LOCK(pwallet->cs_wallet);
    if (!pwallet->GetBroadcastTransactions()) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Error: Wallet transaction broadcasting is disabled with -walletbroadcast");
    }
    std::vector<uint256> txids = pwallet->ResendWalletTransactionsBefore(*locked_chain, GetTime(), g_connman.get());
    UniValue result(UniValue::VARR);
    for (const uint256& txid : txids)
    {
        result.push_back(txid.ToString());
    }
    return result;
}
static UniValue listunspent(const JSONRPCRequest& request)