ZeroNet sometimes hangs

On log messages like:
`[18:29:16] Site:1F7b27..nQpw Announced types ['ip4'] in mode startup to 6 trackers in 10.001s, errors: ['udp://tracker.leechers-paradise.org:6969'], slow: ['10s+ http://tracker.tordb.ml:6881/announce']`
or
`[18:31:19] Site:1F7b27..nQpw Queried listModifications from: [, , , , ]`
zeronet just hangs a long time (~1-5 mins), without responding to requests

Some more log:
```
[18:31:19] Site:1UDbAD..MkoV [FAILED] 87.8.48.197:15441: {'to': 21, 'cmd': 'response', 'error': 'File invalid'}
[18:31:19] Site:1XdLr6..sbrx [FAILED] 83.162.192.96:15442: {'to': 34, 'cmd': 'response', 'error': 'File invalid'}
[18:31:19] FileServer 114.83.43.45 Connect error: error: [Errno 111] Connection refused in ConnectionServer.py line 139 > Connection.py line 100 > _socket2.py line 231
[18:31:19] FileServer Removing Conn#454 114.83.43.45 [?]...
[18:31:19] FileServer Conn#468 192.210.179.116 [v2] > Crypt out connection using: tls-rsa (server side: False)...
[18:31:19] FileServer Conn#516 536zml6mcwrboffk.onion [?] > Connecting...
[18:31:19] TorManager Creating new socket to 536zml6mcwrboffk.onion:15441
[18:31:19] FileServer 223.148.244.101 Connect error: error: [Errno 111] Connection refused in ConnectionServer.py line 139 > Connection.py line 100 > _socket2.py line 231
[18:31:19] FileServer Removing Conn#484 223.148.244.101 [?]...
[18:31:19] FileServer Conn#517 l3s7qjjuechqwjqq.onion [?] > Connecting...
[18:31:19] TorManager Creating new socket to l3s7qjjuechqwjqq.onion:15441
[18:31:19] Site:1UDbAD..MkoV [FAILED] 146.0.226.141:15441: {'to': 32, 'cmd': 'response', 'error': 'File invalid'}
[18:31:19] FileServer 39.187.165.167 Connect error: error: [Errno 111] Connection refused in ConnectionServer.py line 139 > Connection.py line 100 > _socket2.py line 231
[18:31:19] FileServer Removing Conn#445 39.187.165.167 [?]...
[18:31:19] FileServer Conn#518 114.93.100.3 [?] > Connecting...
[18:31:19] FileServer Conn#519 slxwz7fe6m2volyg.onion [?] > Connecting...
[18:31:19] TorManager Creating new socket to slxwz7fe6m2volyg.onion:15441
[18:31:19] FileServer 114.252.75.160 Connect error: error: [Errno 113] No route to host in ConnectionServer.py line 139 > Connection.py line 100 > _socket2.py line 231
[18:31:19] FileServer Removing Conn#433 114.252.75.160 [?]...
[18:31:19] FileServer Conn#520 lfeyaddtybbkwoai.onion [?] > Connecting...
[18:31:19] TorManager Creating new socket to lfeyaddtybbkwoai.onion:15441
[18:31:19] Site:1UDbAD..MkoV [FAILED] 81.101.99.227:15441: {'to': 21, 'cmd': 'response', 'error': 'File invalid'}
[18:31:19] Site:1F7b27..nQpw Queried listModifications from: [, , , , ]
```

possible fix: use multi-threading

Start by tracing the logged connection failures through ConnectionServer.py line 139, Connection.py line 100, and _socket2.py line 231, alongside the tracker and listModifications paths. Reproduce the hang under concurrent peer, tracker, and Tor connections, then verify that ZeroNet continues responding to requests while those operations are slow or failing.

Written by the indexing model from the issue text.