Add a --volume flag to modal shell

[mwaskom]

Supports modal shell --volume ... to quickly attach one (or more) of your volumes to an add-hoc shell for filesystem exploration:

$ modal shell --volume example-models
root@modal:/# ls /mnt/example-models
gpt5.pt  gpt6.pt

You can call it multiple times, like modal shell --volume models --volume data

Volumes are always mounted at /mnt/{name}. I considered making this configurable, e.g. modal shell --volume /mnt/data:my-data-vol. But that felt like overkill for something that targets quick work. If we find a need for it, I think it's fine to expand the interface in the future to allow it. We're reasonably strict about volume names and I think any valid volume name would also be a valid mount point? (Open to counter-arguments here !).

• Closes MOD-2404

Changelog

• Volumes can now be mounted to an ad hoc modal shell session:

  modal shell --volume my-vol-name
  

  When the shell starts, the volume will be mounted at /mnt/my-vol-name. This may be helpful for shell-based exploration or manipulation of volume contents.

  Note that the option can be used multiple times to mount additional models:

  modal shell --volume models --volume data
  

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[charlesfrye]

¿como se llamas?

This is great. I agree on the auto-mounting.

[charlesfrye]

lgtm

[erikbern]

nice!