Add helpers header for working with CPython in C++ tests

[jiridanek]

• Followup to comment on Issue #470 - Fix c-unittests Python object leak introduced in the test #524

[codecov-commenter]

Codecov Report

Merging #526 (c3a9786) into main (6aaadd5) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #526      +/-   ##
==========================================
- Coverage   25.17%   25.17%   -0.01%     
==========================================
  Files         115      115              
  Lines       28771    28771              
  Branches     4669     4669              
==========================================
- Hits         7243     7242       -1     
  Misses      20561    20561              
- Partials      967      968       +1     

Flag	Coverage Δ
unittests	25.17% <ø> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
src/router_core/address_watch.c	78.48% <0.00%> (-1.27%)	⬇️

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