HTTP: intern the version and avoid allocation

[gdamore]

There are only a few possible reasonable values, and we can intern them to avoid any allocations for it. (We will probably do the same for the HTTP method shortly as well.)

fixes #

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[codecov]

Codecov Report

Attention: Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.03%. Comparing base (fc6c4e1) to head (9ac2c5a).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/supplemental/http/http_msg.c	89.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2005      +/-   ##
==========================================
- Coverage   82.06%   82.03%   -0.04%     
==========================================
  Files          95       95              
  Lines       23947    23948       +1     
  Branches     3153     3153              
==========================================
- Hits        19653    19646       -7     
- Misses       4220     4229       +9     
+ Partials       74       73       -1     

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