fix(registrar): ensure onDisconnect is not called when onConnect was skipped for limited connections

[paschal533]

What

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

Problem

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 close, onDisconnect was still being called.

The root cause was 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.

Testing

• Extended existing limited connection test to verify disconnect behavior
• Added test for notifyOnLimitedConnection: true covering both connect and disconnect
• Added test for filter-based topology disconnect logic

Fixes #2647
Fixes #2369