run clang-tidy with C++20

[firewave]

No description provided.

[firewave]

The idea here was that we might be able to address some of the findings by using conditional code.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[danmar]

I created this forum thread:
https://sourceforge.net/p/cppcheck/discussion/development/thread/34ff9ac443/

Please turn off the auto-warnings from clang-tidy it's too pedantic. and then we can use auto where we all agree that it is wanted.

[firewave]

See #8311 (comment) regarding a case of necessary explicit as_const() usage.

[dmcppcheck]

Test results for commit d917aae (tools/test-my-pr.py, main compared to this PR):

Test: http://ec2-16-170-140-253.eu-north-1.compute.amazonaws.com/pr-8188/
packages: 100
Differing warnings: 0 (+0 -0)
Timing: +0.0% (http://ec2-16-170-140-253.eu-north-1.compute.amazonaws.com/pr-8188/2026-02-26_08-45-35-d917aae98bfe_timing.html)

_{Posted automatically by the cppcheck PR test runner. +N: warnings only with this PR, -N: warnings only with main. The AI review is written by Claude and can be wrong.}

[dmcppcheck]

This pull request has merge conflicts that must be resolved.