Implemented median(...) function.

[hazemessamm]

Currently, MLX does not have a bultin median(...) function so I implemented it by using mx.sort(...) and mx.take(...).

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (mlx@587b4c9). Click here to learn what that means.

Files	Patch %	Lines
keras/src/backend/mlx/numpy.py	0.00%	8 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##             mlx   #19568   +/-   ##
======================================
  Coverage       ?   73.71%           
======================================
  Files          ?      506           
  Lines          ?    45809           
  Branches       ?     8466           
======================================
  Hits           ?    33768           
  Misses         ?    10329           
  Partials       ?     1712           

Flag	Coverage Δ
keras	73.56% <0.00%> (?)
keras-jax	59.01% <0.00%> (?)
keras-numpy	53.33% <0.00%> (?)
keras-tensorflow	60.15% <0.00%> (?)
keras-torch	59.08% <0.00%> (?)

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[fchollet]

LGTM, thank you!