mip / package.json: Allow 'deps' to come from another repository

Problem

In repo https://github.com/hmaerki/experiment_micropython_mip, I create a mip-package which may be install as follows:

import mip
mip.install("dryer2023", version="main", index="https://hmaerki.github.io/experiment_micropython_mip")

This is the package.json file:

{
    "version": "0.1",
    "hashes": [
        ["dryer2023/statemachine.mpy", "a47f24f2064b"],
        ["dryer2023/__init__.mpy", "c4104085da6d"]
    ],
    "deps": [
        ["umqtt.simple",  "latest"]     <== ERROR A
        ["https://micropython.org/pi/v2/package/6/umqtt.simple/latest.json",  "dummy"]  <== ERROR B
    ]
}

The installation of the hashes works nice.

In the deps section, I would like to install umqtt.simple from another index (the micropython default) but I could not make it working.

• ERROR A: Will search in my index (https://hmaerki.github.io/experiment_micropython_mip) which is wrong.
• ERROR B: This will correctly download 'latest.json' but then again will try to get the mpy-files from my index which is wrong.

Proposed: Solution

["umqtt.simple", "latest"] should always search in https://micropython.org/pi/v2
["github:org/repo/path/latest.json", "latest"] should search in github:org/repo/path/latest.json

Are there other suggestions/thoughs?

Start by tracing mip.install and the package.json deps handling described in the issue, including how hashes and dependency package URLs are resolved. Done means dependencies can be sourced from the default index or another repository without incorrectly fetching their mpy files from the parent package's index, and the proposed dependency forms behave as specified.