Cache version check for the REST API

[bdraco]

Proposed Changes

validate_server_version was called frequently enough on my low volume systems that rest.py was number 7 in the profile when the system was relatively idle.

Its almost always going to be the same version so it can be cached

before

after

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.27%. Comparing base (a135627) to head (cfe3fbf).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #53      +/-   ##
==========================================
+ Coverage   98.25%   98.27%   +0.02%     
==========================================
  Files           7        7              
  Lines         286      290       +4     
  Branches       19       19              
==========================================
+ Hits          281      285       +4     
  Misses          4        4              
  Partials        1        1              

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