fixes #961 surprising pipe event order

[gdamore]

fixes #

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[gdamore]

This uses a single serialization mutex for ALL pipe callbacks.

Needless to say, this can have an impact for scalability of systems that have vast amounts of churn in the the number of connected pipes (which is an antipattern for NNG btw), or where the pipe event callbacks do non-trivial amounts of work.

It is important that pipe event callbacks finish promptly. Otherwise they can have a pretty bad impact on the overall system. This was true before this logic was added, and it remains true.

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 82.52%. Comparing base (bef6b37) to head (67b4cea).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/core/socket.c	84.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2027      +/-   ##
==========================================
- Coverage   82.63%   82.52%   -0.12%     
==========================================
  Files          95       95              
  Lines       23653    23667      +14     
  Branches     3041     3044       +3     
==========================================
- Hits        19546    19531      -15     
- Misses       4037     4065      +28     
- Partials       70       71       +1     

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