Support non-native project environments

[Vaider7]

Summary

At the current state uv can easily handle non-native platforms on uv sync using --python-platform. But that's actually not the case for non-native environment. For example, if we want to create portable aarch64 environment using conda we cannot use uv to sync packages

Steps to reproduce:

conda create --prefix "$HOME/testpython" -y python=3.13.12 --platform linux-aarch64
conda activate "$HOME/testpython"
export UV_PROJECT_ENVIRONMENT="$HOME/testpython"
uv sync --python-platform aarch64-unknown-linux-gnu --inexact

And it fails with error

error: Failed to query Python interpreter at /home/lisovskiy/testpython/bin/python3
  Caused by: Exec format error (os error 8)

So the solution is to use uv pip install, but it would be really nice if there was a way to manipulate non-native env using uv sync

Example

No response

[zanieb]

We are querying that interpreter to understand, e.g., what Python version it is. I don't think we can feasibly install into an environment without being able to execute the interpreter. We can probably add some overrides that avoid interpreter queries entirely, but that's a big change.