Investigate support for emscripten-forge

[madhur-tandon]

Checklist

• I added a descriptive title
• I searched for other feature requests and couldn't find a duplicate (including also the type-feature tag)
• I confirmed that it's not related to another project area (see the above section)

What is the idea?

This is an epic (umbrella issue) encompassing issues regarding adding support for downloading and installing packages from emscripten-forge (https://github.com/emscripten-forge/recipes) -- which adds a new target i.e. web assembly to build packages through the conda/mamba package managers.

Why is this needed

• We need to support multiple engines i.e. different flavours of python in the browser distributions that come with packages specified by the user in a single environment.
• Currently, only one version of a given extension module can be loaded (but there is support for multiple versions of pure python packages through micropip)
• More information here: https://pyodide.org/en/stable/development/new-packages.html

Adding support for emscripten-forge would enable us to prepare an environment with a python runtime/engine for WASM along with the specified packages with the benefits of dependency resolution, support for multiple versions etc.

What should happen?

• The implementation of py-env tag should probably support adding channels (from which packages have to be searched for) through an attribute.
• The underlying loading of packages should also be dependent on the runtime engine (loadPackage for pyodide for example).
• Which runtime/engine is to be used should probably be specified through the py-config tag.

Additional Context

More details on emscripten-forge available here: https://blog.jupyter.org/mamba-meets-jupyterlite-88ef49ac4dc8