Trace logging

[CAD97]

We should offer a feature (trace, probably, or maybe log) that adds a runtime dependency on log and adds trace! macros to the conversion process. This should help with debugging without having to add manual implementations of FromPest all over the place to trace execution.

[dragostis]

This is something that should probably add to the pest crate as well. Although, I'm not quite sure whether this would be preferable over the debugger work that's already started.

[CAD97]

For pest proper, having a debugger is a huge quality of life thing. For a from-pest conversion, though, I don't know whether a dedicated debugger is practical.

If you're using a tui debugger, I think it should be possible to put breakpoints on <Node as FromPest>::from_pest, though I have to admit ignorance here. I both am spoiled by the IntelliJ Java visual debugger and on Windows, so I have never learned how to use a textual debugger (and really have no desire to).

printf debugging is basic, but simple. Once I can actually use a debugger on Windows (I have a JetBrains license so can use CLion, but have failed multiple times to set it up so far), maybe I can see about improving debuggability that way. But due to the distributed manner of pest-ast (annotations on individual types instead of one localized source of truth), a VM debugger doesn't seem practical.