args: Convert nng_opts_parse into a header only library using `nng_ar…

[gdamore]

…gs_parse`.

The API is identical, except that some names have changed, and this is now a header library in nng/args.h - so the core library does not need to carry this code in binaries. Being a header library also means it is not necessary to link against NNG, and it does not include any parts of NNG; it only depends on a standard C99 or C11 environment.

fixes #

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[codecov]

Codecov Report

Attention: Patch coverage is 97.05882% with 2 lines in your changes missing coverage. Please review.

Project coverage is 83.07%. Comparing base (a40b421) to head (f77e5a5).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/tools/nngcat/nngcat.c	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2069      +/-   ##
==========================================
+ Coverage   82.94%   83.07%   +0.12%     
==========================================
  Files          94       94              
  Lines       23719    23717       -2     
  Branches     3064     3059       -5     
==========================================
+ Hits        19673    19702      +29     
+ Misses       3970     3934      -36     
- Partials       76       81       +5     

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