fix(log): correctly handle errors when logging events

[glevco]

Motivation

This PR contains 2 separate but related fixes that will improve our on-call overhead. They would cause some errors to be logged in multiple unstructured lines, generating several unnecessary alerts.

The first problem was that a bug in string formatting would generate an exception during log event processing, triggering the "error when logging event" path. The second problem was with the logging of this error itself, that was using print statements, and therefore generating the multiple unstructured lines.

This finally resolves https://github.com/HathorNetwork/on-call-incidents/issues/153.

Acceptance Criteria

• Fix incorrect string formatting that caused a KeyError to be raised during logging.
• Remove print() statements when errors occur during logging.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.96%. Comparing base (47831ae) to head (973afe6).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1040      +/-   ##
==========================================
+ Coverage   84.94%   84.96%   +0.02%     
==========================================
  Files         297      297              
  Lines       22906    22906              
  Branches     3463     3463              
==========================================
+ Hits        19457    19462       +5     
+ Misses       2765     2762       -3     
+ Partials      684      682       -2     

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