docs(rust): Fix "forcolumnar" typo in docs

[zero-stroke]

There was a missing space in between "for" and "columnar"

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.96%. Comparing base (127f590) to head (c8bfef5).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #20401   +/-   ##
=======================================
  Coverage   78.96%   78.96%           
=======================================
  Files        1562     1562           
  Lines      220078   220078           
  Branches     2480     2480           
=======================================
+ Hits       173793   173795    +2     
+ Misses      45714    45712    -2     
  Partials      571      571           

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[MarcoGorelli]

thanks @zero-stroke !