feat: Support channel mirrors

[wolfv]

No description provided.

[pavelzw]

What will the pixi lockfile look like then?

Currently, it looks like this:

version: 4
environments:
  default:
    channels:
    - url: https://conda.anaconda.org/conda-forge/
    packages:
      linux-64:
      - conda: https://conda.anaconda.org/conda-forge/linux-64/_libgcc_mutex-0.1-conda_forge.tar.bz2
      - conda: https://conda.anaconda.org/conda-forge/linux-64/_openmp_mutex-4.5-2_gnu.tar.bz2
      - conda: https://conda.anaconda.org/conda-forge/linux-64/backports.zoneinfo-0.2.1-py312h7900ff3_8.conda
      - conda: https://conda.anaconda.org/conda-forge/linux-64/bzip2-1.0.8-hd590300_5.conda
      - conda: https://conda.anaconda.org/conda-forge/linux-64/ca-certificates-2023.11.17-hbcca054_0.conda
      - conda: https://conda.anaconda.org/conda-forge/linux-64/ld_impl_linux-64-2.40-h41732ed_0.conda

When we have multiple mirrors or even URL rewrites, will you still use this format or instead only display the channel name
and platform but not the URL?

One example could be:

version: 4
environments:
  default:
    channels:
    - conda-forge
    packages:
      linux-64:
      - conda: conda-forge/linux-64::_libgcc_mutex=0.1=conda_forge
      - conda: conda-forge/linux-64::_openmp_mutex=4.5-2=gnu
      - conda: conda-forge/linux-64::backports.zoneinfo=0.2.1=py312h7900ff3_8
      - conda: conda-forge/linux-64::bzip2=1.0.8=hd590300_5
      - conda: conda-forge/linux-64::ca-certificates=2023.11.17=hbcca054_0
      - conda: conda-forge/linux-64::ld_impl_linux-64=2.40=h41732ed_0

Since a package is uniquely defined by channel + platform + name + version + build string

[wolfv]

I think we will keep the canonical name (for now). So we would keep https://conda.anaconda.org/conda-forge as the prefix. That's also what is replaced in the mirror so it should work well.

In the future we could come up with other ideas, though.