`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.
#ifndef BITCOIN_BANMAN_H
#define BITCOIN_BANMAN_H
#include <addrdb.h>
#include <bloom.h>
#include <fs.h>
#include <net_types.h> 
#include <sync.h>
#include <chrono>
#include <cstdint>
#include <memory>
static constexpr unsigned int DEFAULT_MISBEHAVING_BANTIME = 60 * 60 * 24; 
static constexpr std::chrono::minutes DUMP_BANS_INTERVAL{15};
class CClientUIInterface;
class CNetAddr;
class CSubNet;
class BanMan
{
public:
    ~BanMan();
    BanMan(fs::path ban_file, CClientUIInterface* client_interface, int64_t default_ban_time);
    void Ban(const CNetAddr& net_addr, int64_t ban_time_offset = 0, bool since_unix_epoch = false);