feat(l1): running some GenServers in dedicated threads

[ElFantasma]

Currently all our GenServers run on the same thread. Many of those are a single process running forever with the application, and may benefit to be run on their own dedicated thread.

This PR moves to their own threads the DiscoveryServer, PeerTableServer and Initiator.

It also improves PeerConnection logging as it moves many debug lines to trace

[github-actions]

Lines of code report

Total lines added: 22
Total lines removed: 0
Total lines changed: 22

Detailed view

+---------------------------------------------------+-------+------+
| File                                              | Lines | Diff |
+---------------------------------------------------+-------+------+
| ethrex/crates/networking/p2p/discv4/peer_table.rs | 916   | +10  |
+---------------------------------------------------+-------+------+
| ethrex/crates/networking/p2p/discv4/server.rs     | 483   | +3   |
+---------------------------------------------------+-------+------+
| ethrex/crates/networking/p2p/rlpx/initiator.rs    | 107   | +6   |
+---------------------------------------------------+-------+------+
| ethrex/crates/networking/p2p/rlpx/utils.rs        | 100   | +3   |
+---------------------------------------------------+-------+------+

[ElFantasma]

Tested on a server on Sepolia with debug_assertions:

2025-10-17T19:50:00.289123Z  INFO ethrex_p2p::network: P2P Snap Sync:
elapsed: 04h 22m 02s 15ms
100 peers.
Current step: Requesting Bytecodes
Current Header Hash: 36e1caefc5e0ce899d7cced9cb3bcf9318657e55601fc870e3c63b3f22eb8215
---
headers progress: 100.00% (total: 9432306, downloaded: 9432324, remaining: 0)
account leaves download: 128745427, elapsed: 00h 00m 55s 00ms
account leaves insertion: 100.00%, elapsed: 00h 10m 04s 00ms
storage leaves download: 651428966, elapsed: 00h 09m 32s 00ms, initially accounts with storage 13565519, healed accounts 9960
storage leaves insertion: 13565519, 00h 46m 02s 02ms
healing: global accounts healed 13719 global storage slots healed 88720, elapsed: 00h 01m 03s 00ms, current throttle \x1b[32mPeers\x1b[0m
bytecodes progress: downloaded: 9764178, elapsed: 00h 14m 21s 00ms)
2025-10-17T19:50:00.916254Z  INFO ethrex_rpc::engine::payload: Received new payload block_hash=0xf349…a3b2 block_number=9433297
2025-10-17T19:50:00.917383Z  WARN ethrex_rpc::engine::payload: Snap sync in progress, skipping new payload validation
2025-10-17T19:50:07.055194Z  INFO ethrex_p2p::sync: Sync cycle finished, time elapsed: 15722 secs

[Arkenan]

This PR may solve #4938

[MegaRedHand]

👍