Add Array API namespace from_dlpack

[dylantirandaz]

Summary

• Add mlx.core.from_dlpack, making it available through array.__array_namespace__()
• Add Array API namespace tests for from_dlpack
• Cover xp.asarray(..., copy=True) through the namespace

Fixes #3484

Testing

• DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer CMAKE_BUILD_PARALLEL_LEVEL=8 python -m pip install -e .
• python -m black --check python/tests/test_array.py
• DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer python -X faulthandler -m unittest test_array.TestArray.test_array_namespace test_array.TestArray.test_array_namespace_asarray test_array.TestArray.test_array_namespace_from_dlpack test_array.TestArray.test_asarray_copy test_array.TestArray.test_dlpack
• git diff --check