Implement hanning function in keras.ops

[shashaka]

Adds keras.ops.hanning, which computes the Hanning window. Supported across NumPy, TensorFlow, PyTorch, and JAX backends, but not supported on OpenVINO.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 84.61538% with 4 lines in your changes missing coverage. Please review.

Project coverage is 82.60%. Comparing base (785c9b0) to head (ef02d17).

Files with missing lines	Patch %	Lines
keras/src/ops/numpy.py	80.00%	1 Missing and 1 partial ⚠️
keras/api/_tf_keras/keras/ops/__init__.py	0.00%	1 Missing ⚠️
keras/api/_tf_keras/keras/ops/numpy/__init__.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #21318   +/-   ##
=======================================
  Coverage   82.60%   82.60%           
=======================================
  Files         565      565           
  Lines       54773    54799   +26     
  Branches     8508     8509    +1     
=======================================
+ Hits        45244    45266   +22     
- Misses       7439     7442    +3     
- Partials     2090     2091    +1     

Flag	Coverage Δ
keras	82.41% <84.61%> (+<0.01%)	⬆️
keras-jax	63.55% <57.69%> (-0.01%)	⬇️
keras-numpy	58.71% <61.53%> (-0.01%)	⬇️
keras-openvino	33.13% <34.61%> (+<0.01%)	⬆️
keras-tensorflow	63.96% <57.69%> (-0.01%)	⬇️
keras-torch	63.62% <57.69%> (-0.01%)	⬇️

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[fchollet]

LGTM, thank you for the contribution!