Refactor/remove older decorators and pydantic logic

[jlnav]

Remove decorators for user functions that only I ever developed/used. Dramatically refactor Pydantic logic now that we don't have to support two major versions of it.

[codecov]

Codecov Report

❌ Patch coverage is 92.90780% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.63%. Comparing base (2a85127) to head (d6ec3b6).
⚠️ Report is 181 commits behind head on develop.

Files with missing lines	Patch %	Lines
libensemble/utils/validators.py	85.07%	7 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1717      +/-   ##
===========================================
+ Coverage    92.57%   92.63%   +0.06%     
===========================================
  Files           81       79       -2     
  Lines         8206     8192      -14     
  Branches      1258     1259       +1     
===========================================
- Hits          7597     7589       -8     
+ Misses         407      400       -7     
- Partials       202      203       +1     

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