Gossipsub: control message every n hearthbeat

What

• Add a p2p Ping whose encoding is equivalent to a Subscribe message with the following payload, where tz1Ke2h7sDdakHJQh8WX4Z372du1KChsksyU is the zero/null address.

  let ping_topic =
    Types.Topic.
      {
        slot_index = 0;
        pkh = Signature.Public_key_hash.zero;
      }

• Add an issue #7768 (closed) to integrate the Ping message when bumping the p2p message version
• Add an issue for implementing metrics for the Ping message #7770 (closed)
• Add periodic emission of Subscribe messages for topics the DAL node is subscribed to every 45s. The chosen value is motivated by the following text.

  (* The ping should be performed by the heartbeat handler at least
     every 45s, hence every [heartbeat_ping_interval] ticks when_
     [heartbeat_interval] = 1s.

     A 45-second ping interval is a reasonable choice as it sits in
     the middle of the commonly recommended 30-60 second range for P2P
     networks.

     This timing provides a good balance between maintaining
     reliable connections and managing network overhead.

     It's frequent enough to detect stale peers before most
     NAT/firewall timeouts (which typically occur after 60-120
     seconds)
  *)

Why

• Improves network resilience by ensuring subscription state remains consistent across peers

How

• Added a new heartbeat interval constant hearbeat_ping_interval set to 180s in terms of hearbeat_interval
• During each heartbeat, check if heartbeat_ticks mod hearbeat_ping_interval = 0
  • If it is, iterate through all connections and emit a Ping message to each peer
• Reuse existing emit_p2p_message function to send the Ping messages

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR