fix: cppcheck warnings in standalone/

[umprayz]

what

• This pull request fixes the cppcheck warnings in all .c, .cpp and .h files within the standalone directory.
• The cppcheck command has been connected into the workflow.

why

• The changes were made based on the result of cppcheck command and the built in checks of the workflow.
• Previously, cppcheck could not find the necessary system and Apache headers, resulting in numerous "missing include" warnings and incorrect analysis.
• With these changes, running cppcheck on the standalone directory now produces zero warnings locally and in CI.

references

• The cppcheck configuration logic in Makefile.am was based on the v3/master branch.

notes

• I would like to continue this work on other directories too and make the whole source tree cppcheck clean.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
8 Accepted issues

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

See analysis details on SonarQube Cloud

[umprayz]

Closing in favour of #3488, which is a cleaner version.