fix(registrar): ensure onDisconnect respects notifyOnLimitedConnection

[paschal533]

Title

fix(registrar): ensure onDisconnect respects notifyOnLimitedConnection

Description

Fixed an inconsistency in topology notification where onDisconnect could fire for connections that never triggered onConnect.

When a topology has notifyOnLimitedConnection unset (default false), connections with limits (like circuit relay connections used for WebRTC SDP signaling) correctly skip onConnect. However, when these connections closed, onDisconnect was still being called due to a logic error in _onDisconnect:

// Before: when topology.filter is undefined, this evaluates to
// undefined === false → false, so the early return never triggers
if (topology.filter?.has(remotePeer) === false) { return }

// After: explicitly checks filter exists before checking membership
if (topology.filter != null && topology.filter.has(remotePeer) !== true) { return }

This caused spurious disconnect events in protocol handlers like GossipSub when WebRTC browser-to-browser connections use temporary relay connections for SDP exchange.

Fixes #2647
Fixes #2369

Notes & open questions

• No changes were needed in transport-webrtc because circuit relay v2 connections already have connection.limits set. The bug was purely in the registrar's disconnect notification logic.
• The optional chaining behavior (undefined === false → false) is a subtle JS gotcha that allowed this to go undetected.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works