`banlist.dat` was introduced in https://github.com/bitcoin/bitcoin/pull/6310, storing nodes that were automatically banned (due to exceeding the misbehavior threshold) and manually banned (through the `setban` RPC).

Automatic bans were removed in https://github.com/bitcoin/bitcoin/pull/19219 and replaced with a discouragement filter. That filter is not saved to disk/persisted over shutdown/startup. The `banlist.dat` therefore now only contains addresses that have been banned through the `setban` rpc.

Since https://github.com/bitcoin/bitcoin/pull/15935, we have a specific file for configuration that is updated through the RPC and persisted over shutdown/startup, namely `settings.json`. We should therefore move the manual ban configuration from `banlist.dat` to `settings.json`. Doing so has a couple of benefits:

- `settings.json` is human readable and easily analyzable by any json parser.
- we wouldn't need to maintain custom [de]serialization code for the `banlist.dat` file.

`banlist.dat` is expected to be fairly small and infrequently updated, so disk space/performance are not huge concerns.
gArgs.ClearPathCache();
    {
        SetupServerArgs(*m_node.args);
        std::string error;
        const bool success{m_node.args->ParseParameters(arguments.size(), arguments.data(), error)};
        assert(success);
        assert(error.empty());
    }
    SelectParams(chainName);
    SeedInsecureRand();
    if (G_TEST_LOG_FUN) LogInstance().PushBackCallback(G_TEST_LOG_FUN);
    InitLogging(*m_node.args);
    AppInitParameterInteraction(*m_node.args);
    LogInstance().StartLogging();
    SHA256AutoDetect();
    ECC_Start();
    SetupEnvironment();
    SetupNetworking();
    InitSignatureCache();
    InitScriptExecutionCache();
    m_node.chain = interfaces::MakeChain(m_node);
    g_wallet_init_interface.Construct(m_node);
    fCheckBlockIndex = true;
    static bool noui_connected = false;
    if (!noui_connected) {
        noui_connect();
        noui_connected = true;
    }
}
BasicTestingSetup::~BasicTestingSetup()