Rez pip error handling improvements

[BryceGattis]

Add error handling for failed resolve and improve error handling if python package not found in resolve

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 58.39%. Comparing base (36e0537) to head (c4bbf81). Report is 12 commits behind head on main.

Files	Patch %	Lines
src/rez/pip.py	0.00%	6 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1734      +/-   ##
==========================================
+ Coverage   58.29%   58.39%   +0.10%     
==========================================
  Files         126      126              
  Lines       17159    17167       +8     
  Branches     3505     3508       +3     
==========================================
+ Hits        10002    10025      +23     
+ Misses       6493     6477      -16     
- Partials      664      665       +1     

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