[main] avoid boxing when @kernel is used as a closure

[simeonschaub]

This allows uses of @kernel inside of functions without running into
JuliaLang/julia#53295.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 47.54%. Comparing base (31dc584) to head (db02850).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/macros.jl	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #627      +/-   ##
==========================================
- Coverage   47.59%   47.54%   -0.06%     
==========================================
  Files          22       22              
  Lines        1727     1729       +2     
==========================================
  Hits          822      822              
- Misses        905      907       +2     

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