refactor(internal): cleanup buildMessage()

[iuioiua]

For improved maintainability.

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 91.48%. Comparing base (c53ca87) to head (086f4ed).

Files	Patch %	Lines
internal/build_message.ts	85.71%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4705   +/-   ##
=======================================
  Coverage   91.48%   91.48%           
=======================================
  Files         477      477           
  Lines       37273    37270    -3     
  Branches     5316     5316           
=======================================
- Hits        34098    34096    -2     
+ Misses       3119     3118    -1     
  Partials       56       56           

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