Add additional diagnostic logging for transfers

[jpdillingham]

This PR adds an additional callback to transfer options and wraps diagnostic statements so that they are sent as typical diagnostics, and the callback. This will allow for all diagnostic messages on an individual transfer record to be grouped and logged together, which is something that is very challenging today when trying to review application behavior under heavy load.

I'm not sure I really need this for the time being, so I'll leave this open in draft mode for now.

[sonarqubecloud]

Quality Gate failed

Failed conditions
77.5% Coverage on New Code (required ≥ 80%)
32.8% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 77.46479% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.43%. Comparing base (bdaa808) to head (9eacfb8).

Files with missing lines	Patch %	Lines
src/SoulseekClient.cs	75.75%	11 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #885      +/-   ##
==========================================
- Coverage   98.64%   98.43%   -0.21%     
==========================================
  Files         184      184              
  Lines        6428     6470      +42     
  Branches      991      997       +6     
==========================================
+ Hits         6341     6369      +28     
- Misses         63       73      +10     
- Partials       24       28       +4     

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