Add support for python 3.12+ and drop support for 3.7

[instinct-vfx]

Fixes #1948. Builds on #1943 as many of the issues are due to outdated vendored dependencies.

[codecov]

Codecov Report

Attention: Patch coverage is 75.60976% with 10 lines in your changes missing coverage. Please review.

Project coverage is 59.93%. Comparing base (4708523) to head (a693974).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rez/utils/pip.py	84.84%	2 Missing and 3 partials ⚠️
src/rez/utils/py_dist.py	0.00%	4 Missing ⚠️
src/rez/bind/rez.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1950      +/-   ##
==========================================
- Coverage   60.02%   59.93%   -0.09%     
==========================================
  Files         163      163              
  Lines       20118    20051      -67     
  Branches     3506     3515       +9     
==========================================
- Hits        12075    12018      -57     
+ Misses       7223     7211      -12     
- Partials      820      822       +2     

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[JeanChristopheMorinPerso]

Thanks @instinct-vfx, I left some comments.

[JeanChristopheMorinPerso]

Tests are now passing. We should still try to install stuff with rez-pip, just in case. Our test suite doesn't have any tests for that.

[JeanChristopheMorinPerso]

Also, this PR technically drops support for Python 3.7 since we use importlib.metadata.