Process profiling and metrics

[Leokuma]

I'm planning to make a Node Exporter plugin for Pup.

I'm also planning to make a Pidusage plugin after porting it for Deno. It's what pm2 uses. It would be a simpler, lightweight, standalone alternative to Node Exporter that could eventually be builtin to Pup's core.

[Hexagon]

Sounds great!!

It's ok to make changes to the plugin interface (and internals) if needed 👍