Kulfi cleanup

[siddhantk232]

This should be done ideally after our work on fastn mail is done (we'll provide more context later) and when we're ready for the launch. It's not blocked on fastn mail since it only depends on fastn-net and fastn-id52 crate which are already there in fastn/v0.5 and published on crates.io. But there's no advantage of doing it right now and:

• The latest malai release still works
• The fix is just a cleanup to reduce the code in malai repo and have it work with latest iroh. It adds no new features.

Motivation

We are not planning to use the branding "Kulfi" as we're focusing on integrating new features directly into fastn. Having "Kulfi" around creates more confusion.

Tasks

• Rename fastn-stack/kulfi -> fastn-stack/malai
• Make malai main branch work with latest iroh (0.91)
• Remove crates kulfi-utils and id52 crate and use fastn-net and fastn-id52 crate from fastn/v0.5
• Make malai binary print fastn bridge urls
• Get rid of the word "Kulfi" from other places