Looks like cat is slower than its GNU counterpart

I tried cat on the following file, prepended with time. And, according to the results, uu-cat is slower than than cat.

emacs.md

Results:

$ time cat emacs.md

________________________________________________________
Executed in  149.81 millis    fish           external
   usr time    0.28 millis    0.28 millis    0.00 millis
   sys time    5.85 millis    1.02 millis    4.82 millis

$ time uu-cat emacs.md

________________________________________________________
Executed in  454.49 millis    fish           external
usr time    4.02 millis    0.00 millis    4.02 millis
sys time   21.83 millis    1.85 millis   19.98 millis

Start by reproducing the attached emacs.md comparison between GNU cat and uu-cat, recording the environment and timing details. Trace the uu-cat entry point and compare its behavior with cat to identify where the extra time occurs; done means a documented cause and a verified performance improvement or explanation.