[OpenVINO Backend] Support: Implemented numpy.diagonal for keras ov backend

[geeky33]

• 1. Implemented a diagonal function similar to diag, handling 2D+ tensors.
• 2. Extracted diagonals based on the given axis1, axis2, and offset (k).
• 3. Used OpenVINO ops like gather or gather_nd to fetch diagonal elements.

Ticket Id:

openvinotoolkit/openvino#29116

Concerned Authority:

CC: @rkazants

[google-cla]

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[geeky33]

Filled the CLA

Apologies
Didn't know I had to do it.

Thanks and Regards.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 3.22581% with 30 lines in your changes missing coverage. Please review.

Project coverage is 82.41%. Comparing base (decd6ba) to head (692c2ce).

Files with missing lines	Patch %	Lines
keras/src/backend/openvino/numpy.py	3.22%	30 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21028      +/-   ##
==========================================
- Coverage   82.45%   82.41%   -0.05%     
==========================================
  Files         562      562              
  Lines       53720    53750      +30     
  Branches     8335     8340       +5     
==========================================
  Hits        44297    44297              
- Misses       7381     7411      +30     
  Partials     2042     2042              

Flag	Coverage Δ
keras	82.23% <3.22%> (-0.05%)	⬇️
keras-jax	63.61% <0.00%> (-0.04%)	⬇️
keras-numpy	58.58% <0.00%> (-0.04%)	⬇️
keras-openvino	32.72% <3.22%> (-0.02%)	⬇️
keras-tensorflow	64.05% <0.00%> (-0.04%)	⬇️
keras-torch	63.65% <0.00%> (-0.04%)	⬇️

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[rkazants]

@geeky33, you have a lot of unneeded changes in PR:

do NOT merge!!!