Disable env access and file load operations in yqlib

[jandubois]

Before:

❯ l ls --yq 'env(HOME)'
/Users/jan

❯ l ls --yq 'load("/usr/local/share/lima/templates/ubuntu.yaml")'
{
    "minimumLimaVersion": "2.0.0",
    "base": [
        "template:_images/ubuntu-25.10",
        "template:_default/mounts"
    ]
}

After:

❯ l ls --yq 'env(HOME)'
FATA[0000] env operations have been disabled

❯ l ls --yq 'load("/usr/local/share/lima/templates/ubuntu.yaml")'
FATA[0000] file operations have been disabled

Addresses objections to using YQ expressions for limactl list --filter in #4187.

[AkihiroSuda]

I think we can allow --yq to access env, as long as the upstream yq continues to allow accessing env by default.

The proposed --filter should be restrictive though

[jandubois]

I think it is best to restrict it everywhere, except for limactl yq itself.

What is the use case for limactl list --yq or limactl info --yq to use env variables or load from files?

[jandubois]

I continue to think that having just a single flavour of YQ expressions throughout Lima is preferable, especially since there are no known use-cases for the prohibited operations. Otherwise you have to document the kind of expression allowed separately for each option that takes a YQ expression.

And you can still do this if you really want to:

limactl list --json | limactl yq '...'

Because the yq command itself is not limited, only any expression used in Lima internally.