Consider making the max width / height of infoviews work via percentages of real estate rather than columns/rows

For narrow screens -- such as the one used for [the demo script (especially with even smaller dimensions)](https://github.com/Julian/lean.nvim/blob/main/demos/basic.tape) -- the infoview even at max width can seem to take up a full half of the available space, which is unnecessary.

It might be better if this max width was a percentage of the available columns, and then we set it to 1/3 or something.

This may really be about making both possible (a la CSS) to configure, and then changing the default to percentage-based.