Make --universal and --python-platform mutually exclusive

[charliermarsh]

Summary

Open to just making this a warning but no strong opinion.

Closes #4593.

Test Plan

Failure:

❯ echo "pandas==2.2.2" | cargo run pip compile --universal -p 3.11 --no-header - --python-platform linux
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.15s
     Running `target/debug/uv pip compile --universal -p 3.11 --no-header - --python-platform linux`
error: the argument '--universal' cannot be used with '--python-platform <PYTHON_PLATFORM>'

Usage: uv pip compile --universal --python-version <PYTHON_VERSION> --no-header <SRC_FILE>...

For more information, try '--help'.

[charliermarsh]

I think I'll just make it a warning, shrug.

[zanieb]

If a warning, we ignore the python-platform entirely?

[charliermarsh]

Yeah we ignore it either way.

[zanieb]

Let's error then.

[charliermarsh]

Ok, fine with me.