Add INetMQMonitor interface to enable mocking in tests

[Copilot]

This PR adds an INetMQMonitor interface to allow mocking of NetMQMonitor in tests, similar to the existing INetMQSocket and INetMQPoller interfaces.

Changes Made

1. Created INetMQMonitor interface (src/NetMQ/Monitoring/INetMQMonitor.cs) containing all public members of NetMQMonitor:

   • Properties: Endpoint, IsRunning, Timeout
   • Events: All monitoring events (Connected, Listening, Accepted, etc.)
   • Methods: AttachToPoller, DetachFromPoller, Start, StartAsync, Stop, Dispose
   • Documentation describes the abstraction: "Monitors a NetMQSocket for events, raising them via events"

2. Updated NetMQMonitor to implement INetMQMonitor interface with <inheritdoc /> tags throughout to inherit documentation from the interface

3. Deleted NuGet.Config file as it only contained the default NuGet.org package source and is no longer needed

Documentation

All XML documentation follows best practices:

• Property docs start with "Gets" or "Gets and sets"
• All summaries end with periods
• Uses <see cref="..." /> when referring to symbols
• No duplicate documentation between interface and implementation

Testing

• ✅ Build succeeds with 0 warnings, 0 errors
• ✅ All changes are non-breaking - existing code continues to work unchanged

Fixes #1137

Original prompt

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This section details on the original issue you should resolve

<issue_title>There is no interface on the NetMQMonitor allowing us to mock it during testing</issue_title>
<issue_description>There are the interfaces INetMQSocket and INetMQPoller allowing us to mock them for testing but there isn't one for the monitor. Currently we have to create an adapter just to mock it, it'd be handy to have the interface. I'm happy to help implement it if required.</issue_description>

Comments on the Issue (you are @copilot in this section)

@drewnoakes Feel free to submit a PR! It should be possible to achieve this without breaking anyone.

Fixes #1137

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[drewnoakes]

@copilot PTAL

[drewnoakes]

@djangohunt does this look good to you? Happy with the members on the interface?

[drewnoakes]

@copilot please improve the docs as described.

[Copilot]

@copilot please improve the docs as described.

Done in commit 9c4e6bf. All documentation improvements have been applied as described in the review comments.