Implement nanpercentile function in keras.ops

[shashaka]

Description

Adds keras.ops.nanpercentile, which computes the q-th percentile of the input tensor along a specified axis while ignoring NaN values.
Supported across NumPy, TensorFlow, PyTorch, and JAX backends. Not supported on OpenVINO.

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[gemini-code-assist]

Code Review

This pull request implements the nanpercentile operation across Keras backends, including JAX, NumPy, TensorFlow, and Torch, while marking it as unimplemented for OpenVINO. The implementation includes the core Nanpercentile operation, API exports, and extensive unit tests. Feedback focuses on improving the robustness of compute_output_spec regarding multi-dimensional percentile inputs and integer dtype promotion, as well as ensuring consistent tensor conversion and floating-point casting of the q parameter across the NumPy and Torch backends.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.79592% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.00%. Comparing base (90e0c5e) to head (5209df1).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
keras/src/ops/numpy.py	87.50%	2 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   #22679   +/-   ##
=======================================
  Coverage   82.99%   83.00%           
=======================================
  Files         596      596           
  Lines       69629    69678   +49     
  Branches    10863    10869    +6     
=======================================
+ Hits        57792    57836   +44     
- Misses       8991     8995    +4     
- Partials     2846     2847    +1     

Flag	Coverage Δ
keras	82.82% <89.79%> (+<0.01%)	⬆️
keras-jax	58.43% <61.22%> (+<0.01%)	⬆️
keras-numpy	54.29% <69.38%> (+0.01%)	⬆️
keras-openvino	59.67% <44.89%> (-0.02%)	⬇️
keras-tensorflow	59.99% <61.22%> (+<0.01%)	⬆️
keras-torch	58.76% <61.22%> (+<0.01%)	⬆️

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[hertschuh]

Thanks!

But I'm realizing now that we don't even have ops.numpy.percentile right now.

[shashaka]

I’ll take a look and add a implementation for ops.numpy.percentile.