formatting of nep-18 compatible arrays with assert_*

[keewis]

At the moment, the formatting.diff_*_repr functions that provide the pretty-printing for assert_* use repr to format NEP-18 strings, truncating the result if it is too long. In the case of pint's quantities, this makes the pretty printing useless since only a few values are visible and the unit is in the truncated part.

What should we about this? Does pint have to change its repr?

xref #3611

[keewis]

oh, sorry, maybe this is a duplicate of #2773?

[TomNicholas]

maybe this is a duplicate

Yeah it basically is now that unitful arrays are nearly ready - let's discuss it there instead.