implement --invert for pip tree

[ChannyClaus]

Summary

partially resolves #4439

Test Plan

existing tests pass + added a couple of new tests with --invert.

[ibraheemdev]

Can you add a test to see how --invert interacts with --no-dedupe? After that this looks good to me.

[ChannyClaus]

all done 🌵

[Peiffap]

I haven't looked at the implementation in detail, but is there a reason we want this to be --invert instead of --reverse like in pipdeptree?

[ChannyClaus]

I haven't looked at the implementation in detail, but is there a reason we want this to be --invert instead of --reverse like in pipdeptree?

no reason, i just followed the naming convention in cargo tree, but if there's an overall preference for --reverse i'm happy to rename 👍

[zanieb]

I kind of find --invert clearer, but we can provide a hidden alias --reverse for pipdeptree compatibility.