[enhancement] trace_fmt should support formatting u8[N] as strings

### What's hard to do? (limit 100 words)

currently printing a `u8[N]` w/ trace_fmt and `{}` result in printing the underlying u8 array, making it challening to display data-driven trace labels in table-based test function.

### Current best alternative workaround (limit 100 words)

none that I know of.

### Your view of the "best case XLS enhancement" (limit 100 words)

ideally we have a new format directive `{:s}` that interpret and print the underlying `u8[N]` as a string