streams: add explicit stop functions

[gdamore]

This allows us to explicitly stop streams, dialers, and listeners, before we start tearing down things. This hopefully will be useful in resolving use-after-free bugs in http, tls, and websockets.

The new functions are not yet documented, but they are nng_stream_stop, nng_stream_dialer_stop, and nng_stream_listener_stop. They should be called after close, and before free. The close functions now close without blocking, but the stop function is allowed to block.

fixes #

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[codecov]

Codecov Report

Attention: Patch coverage is 92.61084% with 15 lines in your changes missing coverage. Please review.

Project coverage is 81.73%. Comparing base (90308d8) to head (81f5d3c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/platform/posix/posix_tcpdial.c	50.00%	4 Missing ⚠️
src/core/sockfd.c	25.00%	3 Missing ⚠️
src/platform/posix/posix_ipcdial.c	70.00%	3 Missing ⚠️
src/core/tcp.c	90.90%	2 Missing ⚠️
src/platform/posix/posix_ipclisten.c	93.33%	1 Missing ⚠️
src/platform/posix/posix_tcplisten.c	85.71%	1 Missing ⚠️
src/sp/transport/ws/websocket.c	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1987      +/-   ##
==========================================
- Coverage   81.87%   81.73%   -0.15%     
==========================================
  Files          95       95              
  Lines       24094    24232     +138     
  Branches     3201     3208       +7     
==========================================
+ Hits        19728    19805      +77     
- Misses       4293     4355      +62     
+ Partials       73       72       -1     

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