refactor(nu-hooks/startup-times): Better performance and UX

[Bahex]

• Use attr based examples.
• Hook removes itself after running, rather than staying loaded.
• Switch to tsv as storage format to allow adding new logs without loading the file into memory.

[fdncred]

Seems reasonable. I've ran a custom version of this since Aug-2023. My windows system is horribly slow but here's what I do with the output of a script like this one. I thought "perf per byte" would be a reasonable way to measure performance since everyone sources/uses different files at startup. I could share my startup-stats script too if anyone is interested.