Make sentry-sdk[pure-eval] installable with pip==24.0

[sentrivana]

There's an issue with pip==24.0 where extras with an underscore in the name can't be installed, so e.g. pip install sentry-sdk[pure_eval] will claim there is no pure_eval extra.

The issue is fixed in pip>=24.1. Some folks are stuck using older versions though. We can fix it for them by renaming the extra to pure-eval instead, which makes pip install sentry-sdk[pure-eval] work correctly in 24.0 too.

(The underscore version sentry-sdk[pure_eval] will continue to work after this change. Tested with pip and uv.)

Closes #3754

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.38%. Comparing base (200d0cd) to head (a5b8f1b).

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3757      +/-   ##
==========================================
+ Coverage   84.37%   84.38%   +0.01%     
==========================================
  Files         136      136              
  Lines       14375    14375              
  Branches     2422     2422              
==========================================
+ Hits        12129    12131       +2     
  Misses       1495     1495              
+ Partials      751      749       -2     

see 2 files with indirect coverage changes