Feature request: Add Jujutsu (jj) support #271

Summary

Add support for Jujutsu (jj), a Git-compatible VCS that's gaining popularity among developers.

Motivation

jj commands produce output very similar to git — jj status, jj diff, jj log are analogous to their git counterparts. Since rtk already compresses git output effectively, adding jj support should be straightforward.

Suggested subcommands

Workaround

Currently, jj commands pass through without compression. There's no hook-level workaround since the compression logic lives in the rtk binary.

Additional context

Jujutsu uses Git as its storage backend, so the output formats are very close to Git's. The existing git formatters may work with minimal adaptation.