[Magic CLI]: nodefaults not properly handled in environment.yml

[comods]

Issue description

See https://github.com/conda/conda-lock/pull/418

If an environment.yml file has a channel that is nodefaults, this isn't suppose to be appended to conda-forge's url. It is suppose to mean, do NOT use any channels outside the environment.yml file, like conda-forge.

Steps to reproduce

Try to use the environment.yml created by: https://github.com/quantco/pixi-pack

magic --no-progress init --import "environment.yml"

Workaround is to create a copy of the .yml file with nodefaults stripped out and to change some berried magic configs.

ERROR error=repodata not found
ERROR error=repodata not found
ERROR error=could not find subdir 'noarch' in channel 'https://conda.anaconda.org/nodefault/'
  × could not find subdir 'noarch' in channel 'https://conda.anaconda.org/
  │ nodefault/'
  ╰─▶ HTTP status client error (404 Not Found) for url (https://
      conda.anaconda.org/nodefault/noarch/repodata.json)

Version Info

Linux fd2037a033db 5.15.154+ x86_64
jupyter_client   : 8.6.2
jupyter_core     : 5.7.2
traitlets        : 5.14.3
magic 0.2.2
conda 24.7.1
max 24.4.0 (59977802)
Modular version 24.4.0-59977802-release
mojo 24.4.0 (59977802)
Python 3.11.9