feat: would like table.add to toString by default

[eseidel]

Similar to how print() works, etc. Just calls toString on the object.
https://github.com/dart-lang/sdk/blob/main/sdk/lib/core/print.dart#L19

I think this should be doable by making Table.add take Object? rather than dynamic?

Right now if you pass an object instead of a string, it just leaves the cell blank it seems, which seems like the wrong default?