load metallib not only as resource but in root of a bundle

[gin66]

Proposed changes

This is in relation to mlx-swift. MetalCompilerPlugin does not generate a resource, but stores the lib in the bundle root. This patch adds bundle root to the search locations for the default.metallib.

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[davidkoski]

I think we should hold onto this until we discuss on the mlx-swift side. I am concerned that this works around a build issue in the metal builder plugin -- perhaps we should just figure out how to get that to produce the correct path.

See also ml-explore/mlx-swift#313

[gin66]

I would appreciate to get this implemented. It has no negative side effects and the code after my comment could be kept, even though I wonder, if this is a leftover of an older code basis.