feat: add addClassToHast to transformer context

[antfu]

Due to the high frequency this function is used, it's better to expose it directly in the context to make the usage similar and avoid accidentally introducing unnecessary deps

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d123b4b) 96.94% compared to head (7a2f327) 96.94%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #573   +/-   ##
=======================================
  Coverage   96.94%   96.94%           
=======================================
  Files          55       55           
  Lines        5173     5178    +5     
  Branches      657      657           
=======================================
+ Hits         5015     5020    +5     
  Misses        154      154           
  Partials        4        4           

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