Recommend `:text` instead of `:string`

I _know_ this but I need to find the right sources to cite and run my own benchmarks.

Here's a wonderful start: https://www.depesz.com/2010/03/02/charx-vs-varcharx-vs-varchar-vs-text/

It's not so much a caution of "don't do this" but more of a "steer in better direction with no trade-offs".

