`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.
: ChainTestingSetup(chainName, extra_args)
{
    const CChainParams& chainparams = Params();
    
    
    RegisterAllCoreRPCCommands(tableRPC);
    m_node.chainman->InitializeChainstate(*m_node.mempool);
    m_node.chainman->ActiveChainstate().InitCoinsDB(
         1 << 23,  true,  false);
    assert(!m_node.chainman->ActiveChainstate().CanFlushToDisk());
    m_node.chainman->ActiveChainstate().InitCoinsCache(1 << 23);
    assert(m_node.chainman->ActiveChainstate().CanFlushToDisk());
    if (!m_node.chainman->ActiveChainstate().LoadGenesisBlock(chainparams)) {
        throw std::runtime_error("LoadGenesisBlock failed.");
    }
    BlockValidationState state;
    if (!m_node.chainman->ActiveChainstate().ActivateBestChain(state, chainparams)) {
        throw std::runtime_error(strprintf("ActivateBestChain failed. (%s)", state.ToString()));
    }
    m_node.addrman = std::make_unique<CAddrMan>();
    m_node.banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist.dat", nullptr, DEFAULT_MISBEHAVING_BANTIME);
    m_node.connman = std::make_unique<CConnman>(0x1337, 0x1337, *m_node.addrman); 
    m_node.peerman = PeerManager::make(chainparams, *m_node.connman, *m_node.addrman,
                                       m_node.banman.get(), *m_node.scheduler, *m_node.chainman,
                                       *m_node.mempool, false);
    {
        CConnman::Options options;