Make cpu binary_op easily accessible

[angeloskath]

Similar to the GPU side of things this moves the high level binary(...) into mlx::core renamed as binary_op_cpu and comparison_op_cpu etc.

The point is to simplify things like the one in matmul.cpp. Not many around so maybe we don't want to merge if we thing this pollutes the namespace (but we have all the lower-level stuff in mlx::core 🤷‍♂️ )

[awni]

Nice. I like the consistency.

Seems like we are converging on a scheme like ``op_{cpu|gpu}{_inplace}( ...)` for back end ops that need to be used during eval.

[angeloskath]

Seems like we are converging on a scheme like ``op_{cpu|gpu}{_inplace}( ...)` for back end ops that need to be used during eval.

Yeah exactly. On that note, I should have asked on the main one. Should I rename binary_float_cpu to binary_float_op_cpu ? Which one do you like best. Rethinking it I think I should ...

[awni]

I would vote for consistency for sure. I kind of prefer just binary as opposed to binary_op (which is what we have for unary for CPU. But then for metal it's all unary_op, binary_op, etc.