Change header for show method from time to t.

[artkuo]

show(interp) currently displays a table with headers time and u. The actual struct fields are t and u, described in the docs as "time" and "data," respectively. I find it confusing because most other tables show the property name. Here it tempts me to try interp.time which does not exist.

I propose that the header be changed to t, for consistency with u.

Checklist

• all tests still pass, no new tests needed or added
• does not harm public API
• no documentation changes needed or performed
• The new code follows contributor guidelines

Additional context

An alternative solution would be to update the u header to say "data," so that both headers are qualitative descriptors rather than identifiers.

Technically show labels multidimensional data as u1, u2, etc. which also are not actual identifiers. I think this is reasonable shorthand, lacking a clearly better alternative. Also, the docs mainly emphasize one-dimensional data where u header is strictly correct.