fixes #1408 Reference count as a first class type

[gdamore]

This starts by using this for the nni_pipe, but we will use it for the other primary objects as well. This should simplify the tear down and hopefully eliminate some races.

It does mean that pipe destruction goes through an additional context switch, for now at least. This shouldn't be on the hot data path anyway.

fixes #

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.93%. Comparing base (513f9d1) to head (755dcb2).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1963      +/-   ##
==========================================
+ Coverage   81.75%   81.93%   +0.18%     
==========================================
  Files          94       95       +1     
  Lines       24015    24022       +7     
  Branches     3202     3200       -2     
==========================================
+ Hits        19633    19683      +50     
+ Misses       4311     4265      -46     
- Partials       71       74       +3     

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