test: adding certificate precedence ordering

[Freyskeyd]

Description

This PR adds tests regarding the precedence management and how it behaves for the API.

The context is to test which certificate is returned when call the get_latest_pending_certificate method when the storage contains one or more certificate in the precedence_pool.

PR Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (38cc514) 62.61% compared to head (215aa1f) 62.64%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #375      +/-   ##
==========================================
+ Coverage   62.61%   62.64%   +0.02%     
==========================================
  Files         218      219       +1     
  Lines       11876    11880       +4     
==========================================
+ Hits         7436     7442       +6     
+ Misses       4440     4438       -2     

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