ci: install CodeChecker from PyPI

[jpnurmi]

Caution

Turns out the historical ~30-minute Snap jobs were false greens: every CodeChecker invocation said "No analysis is required" because ldlogger.so failed to preload. There were 19k preload errors and zero actual analyses in a recent successful Snap jobs.

The Snap Store not only has an awfully old CodeChecker 6.21 (Nov 11, 2022) but also intermittently fails otherwise unrelated CI jobs.

Linux (GCC 13.3.0 + code-checker + valgrind:

• https://github.com/getsentry/sentry-native/actions/runs/31701697939/job/94452150918
• https://github.com/getsentry/sentry-native/actions/runs/31698949201/job/94443121258
• https://github.com/getsentry/sentry-native/actions/runs/31698894392/job/94442943079
• https://github.com/getsentry/sentry-native/actions/runs/31698725425/job/94444027678
• ...

error: cannot perform the following tasks:
- Fetch and check assertions for snap "snapd" (27591) (cannot fetch assertion: got unexpected HTTP status code 503 via GET to "https://api.snapcraft.io/v2/assertions/snap-revision/e7IycB54u7-1wMNfkcwkpfowURR3lBAOjv3NeI47ouqkM9qivM3qJvSvQCFLsGxH?max-format=0")

or

error: cannot perform the following tasks:
- Ensure prerequisites for "codechecker" are available (cannot install snap base "core18": Post "https://api.snapcraft.io/v2/snaps/refresh": net/http: request canceled (Client.Timeout exceeded while awaiting headers))

This PR installs a working CodeChecker from PyPI. First of all, there are quite a few findings to either fix or suppress. Secondly, invoking CodeChecker via cmake.py is wrong because it repeatedly reanalyzes the whole project for every test build. The CI round would take several hours, so it needs to be moved into a separate job instead.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.29%. Comparing base (dcf9623) to head (5e305f3).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1991      +/-   ##
==========================================
- Coverage   74.31%   74.29%   -0.03%     
==========================================
  Files         104      104              
  Lines       25638    25638              
  Branches     4627     4627              
==========================================
- Hits        19054    19047       -7     
- Misses       5281     5289       +8     
+ Partials     1303     1302       -1     

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