General performance concerns with large dataclips

[stuartc]

When pairing with @mtuchi we noted some pretty significant performance issues when viewing a large output dataclip.

There isn't much in the way of performance optimisations for viewing these things and there is a significant amount of parsing and formatting going on.

Using a tool like Benchee and a few tests we must describe the performance profile of viewing dataclips and either optimise the formatter or change the UI to limit how much is shown (or both).