[#24281] Normalized '%Z' formatting to UTC offset across platforms

[Danipiza]

Description

This PR makes timezone formatting deterministic in timestamp_to_string by replacing %Z with a computed UTC offset string (UTC+HH or UTC+HH:MM) before calling std::put_time.

Problem

%Z is platform-dependent:

• Windows may return localized full timezone names
• Linux commonly returns short abbreviations (e.g., CET)

This causes inconsistent outputs across OSes for the same formatting pattern.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 21.62162% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.69%. Comparing base (355e332) to head (c29e243).

Files with missing lines	Patch %	Lines
cpp_utils/src/cpp/time/time_utils.cpp	21.62%	10 Missing and 19 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #151      +/-   ##
==========================================
- Coverage   60.41%   59.69%   -0.72%     
==========================================
  Files          65       65              
  Lines        1945     1980      +35     
  Branches      552      580      +28     
==========================================
+ Hits         1175     1182       +7     
- Misses        449      458       +9     
- Partials      321      340      +19     

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