Fix MISRA C 2012 deviations

[chinglee-iot]

Description

• Fix rule 18.4 deviations. Not using operators with pointer type.
• Suppress rule 20.5 deviations in misra.config to allow use of undef.

Test Steps

Checklist:

• I have tested my changes. No regression in existing tests.
• I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (640dd3f) 94.02% compared to head (b039d06) 94.02%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #190   +/-   ##
=======================================
  Coverage   94.02%   94.02%           
=======================================
  Files           3        3           
  Lines        1690     1690           
  Branches      442      442           
=======================================
  Hits         1589     1589           
  Misses         17       17           
  Partials       84       84           

Flag	Coverage Δ
unit_tests	94.02% <100.00%> (ø)

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[Skptak]

Will this repo need the same change to the CI build as coreMQTT's ci.yml file?

Will it also need its unit test version bumped up as was done in coreMQTT/test/CMakeList.txt?

[chinglee-iot]

This project already defined UINT_TESTS and COVERITY option in test/CMakeLists.txt. Another PR will be created to align the test/CMakeLists.txt.