refactor(ini): simplify stringify()

[timreichen]

This PR moves all stringify functionality from IniMap into the stringify() function.
There is a load of unnecessary overhead generated the way stringify() works in IniMap.

Together with #6512 IniMap will become obsolete and can be removed afterwards.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.09%. Comparing base (61f9fd3) to head (6dc1cd0).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6514      +/-   ##
==========================================
- Coverage   95.29%   95.09%   -0.21%     
==========================================
  Files         576      576              
  Lines       43315    43329      +14     
  Branches     6477     6460      -17     
==========================================
- Hits        41279    41204      -75     
- Misses       1995     2084      +89     
  Partials       41       41              

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[kt3k]

Can you reduce unrelated changes (in @std/encoding)?

[timreichen]

Can you reduce unrelated changes (in @std/encoding)?

Done

[kt3k]

LGTM. Thanks!