When importing a watch-only address over `importmulti` with a specific timestamp, the wallet's `nTimeFirstKey` will be set to 1.
I think we should add a optional timestamp to `CWallet::AddWatchOnly()` and use it when importing addresses or pubkeys.

{
    LockedPool::Stats stats = LockedPoolManager::Instance().stats();
    UniValue obj(UniValue::VOBJ);
    obj.push_back(Pair("used", uint64_t(stats.used)));
    obj.push_back(Pair("free", uint64_t(stats.free)));
    obj.push_back(Pair("total", uint64_t(stats.total)));
    obj.push_back(Pair("locked", uint64_t(stats.locked)));
    obj.push_back(Pair("chunks_used", uint64_t(stats.chunks_used)));
    obj.push_back(Pair("chunks_free", uint64_t(stats.chunks_free)));
    return obj;
}
UniValue getmemoryinfo(const JSONRPCRequest& request)