[CI] upgrade to clang-tidy 20

[dbarker]

Fixes #3538

To run clang-tidy on all header files we need to upgrade to version 20.1.0. This version adds the --exclude-header-filter argument enabling analysis of all project header files excluding the api/.../internal/absl headers.

Changes

• upgrade the clang-tidy CI workflow and devcontainer to clang-tidy version 20 from version 18

For significant contributions please make sure you have completed the following items:

• [ ] CHANGELOG.md updated for non-trivial changes
• [ ] Unit tests have been added
• [ ] Changes in public API reviewed

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 89.95%. Comparing base (bed305f) to head (be9b574). :warning: Report is 23 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3762      +/-   ##
==========================================
+ Coverage   89.95%   89.95%   +0.01%     
==========================================
  Files         225      225              
  Lines        7158     7163       +5     
==========================================
+ Hits         6438     6443       +5     
  Misses        720      720              

see 5 files with indirect coverage changes

:rocket: New features to boost your workflow:

• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[marcalff]

@dbarker

The generated reports (seen in CI) are very nice.