add thin logging shim

[davidkoski]

Proposed changes

See ml-explore/mlx-swift-lm#535 (comment)

mlx-swift and related sometimes (rarely) wants to log something. We never picked a solution, and I don't want to lock people in to any particular solution. This adds a very thin logging shim that looks similar to swift-log and has a default OSLog/stderr implementation. Developers can integrate whatever they want and MLX code can now log things if needed.

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)

[nwh]

Nice! The API is also similar to conventional Python logging. eg

import logging
logger = logging.getLogger(__name__)

def foo():
    logger.info("foo was called")