fix: correct reversed arguments in warnings.warn call

[nishantharkut]

Summary

This PR fixes the deprecated compatibility wrapper so warning emission works correctly.

Problem

The warnings.warn positional arguments were reversed. That makes Python treat a string as the warning category, which raises:
TypeError: category must be a Warning subclass, not 'str'.

Changes

1. Put the warning message in the first argument position.
2. Pass DeprecationWarning as the category.
3. Add stacklevel=2 so the warning location points to caller code.
4. Add a focused regression test for warning category, message text, and caller location behavior.

Validation

1. Utility tests pass locally.
2. Lint checks pass locally for the changed files.

[Copilot]

Pull request overview

This PR fixes a deprecated compatibility wrapper so that deprecation warnings are emitted correctly (message/category order and caller location), and adds a regression test to validate the warning behavior.

Changes:

• Fix warnings.warn call argument order and add stacklevel=2 for correct caller attribution.
• Add a regression test to validate warning category, message content, and reported filename.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
xarray_subset_grid/utils.py	Corrects warnings.warn usage in the deprecated assign_ugrid_topology wrapper and sets stacklevel=2.
tests/test_utils.py	Adds a focused test to assert the wrapper emits a DeprecationWarning and points at the caller location.

Comments suppressed due to low confidence (1)

xarray_subset_grid/utils.py:108

• from .grids.ugrid import assign_ugrid_topology rebinds the local name to a different function with the same name as this deprecated wrapper. That works, but it makes stack traces/debugging confusing and is easy to misread as recursion. Consider importing with an alias (e.g., _assign_ugrid_topology) and returning that instead.

        stacklevel=2,
    )
    from .grids.ugrid import assign_ugrid_topology

    return assign_ugrid_topology(*args, **kwargs)

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.