feat(exec): accept relative paths

[tdejager]

Description

This allows for passing of relative parts to exec. As an example:

From this PR

# replace with your platform
cargo r exec -s "./tests/data/channels/channels/non_self_expose_channel_2/osx-arm64/jupyter-core-0.2.0-h60d57d3_0.conda" python

Python 3.13.5 | packaged by conda-forge | (main, Jun 16 2025, 08:24:05) [Clang 18.1.8 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

This useful for testing out local conda files you have just build using pixi build, this was already possible with absolute paths.

The question is how to solve this, doing this in rattler would require accesing the pwd while parsing, which is not ideal. I opted to go for a typed data-structure here. I'm keeping it in draft until we are sure this makes sense. I think the downside of this approach is that it adds a lot of code, we can also add a clap parser, but that does not make this explicitly in the type.

Fixes: #4867 (by adding relevant tests)

How Has This Been Tested?

Manually, and a number of tests have been added.

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

I made the initial idea and codex worked it out for me.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added sufficient tests to cover my changes.
• I have verified that changes that would impact the JSON schema have been made in schema/model.py.

[tdejager]

might be good to add more cases here if we know m?

[tdejager]

An additional comment.

[baszalmstra]

This looks really good to me!