Allow additional args to be passed many times

[gpupuck]

This would allow

-a "scan_layers=false max_target_length=4096 use_iota_embed=true logits_dot_in_fp32=false"

to be

-a scan_layers=false 
-a max_target_length=4096 
-a use_iota_embed=true 
-a logits_dot_in_fp32=false

It will help avoid issues if quotes are not present during string interpolation.

[kocchop]

@gpupuck all the maxtext CI tests are failing