Add array API standard aliases for existing ops

[katlun-lgtm]

Proposed changes

array.__array_namespace__() returns the mlx.core module, so array API conformance depends on mlx.core exposing the array API standard names. Several elementwise ops are currently only available under their numpy-style names. This adds spec-conformant aliases that forward to the existing operations:

array API name	forwards to
acos, acosh, asin, asinh, atan, atanh	arccos, arccosh, arcsin, arcsinh, arctan, arctanh
atan2	arctan2
pow	power
bitwise_left_shift, bitwise_right_shift	left_shift, right_shift

Each alias is a thin forwarder following the existing concat -> concatenate precedent, is added to the ops documentation, and is covered by a new test (test_array_api_aliases) that checks output equality with the originals and presence on the __array_namespace__() object.

This is a focused first step toward #3484. (asarray / asarray(copy=) from that issue already landed on main; from_dlpack and other gaps remain for follow-ups.)

Checklist

• I have read the CONTRIBUTING document
• clang-format and black (the formatters configured in .pre-commit-config.yaml) report no changes on the modified files
• Added a test (python/tests/test_ops.py::TestOps::test_array_api_aliases)
• Built from source and ran python -m unittest test_ops locally — all 140 tests pass; the existing __array_namespace__ tests in test_array.py also pass