[OpenVINO Backend] support ops.slice_update

[Mohamed-Ashraf273]

Hi @rkazants ,
I've supported ops,silce_update for my GSoC project, but I can't enable tests for it until getting __getitem__ merge.

It could be implemented more easily if we use opset15 instead of opset14.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.15686% with 4 lines in your changes missing coverage. Please review.

Project coverage is 82.82%. Comparing base (d55a767) to head (8093d51).

Files with missing lines	Patch %	Lines
keras/src/backend/openvino/core.py	92.15%	1 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21362      +/-   ##
==========================================
+ Coverage   82.81%   82.82%   +0.01%     
==========================================
  Files         565      565              
  Lines       55520    55571      +51     
  Branches     8664     8673       +9     
==========================================
+ Hits        45977    46025      +48     
- Misses       7428     7429       +1     
- Partials     2115     2117       +2     

Flag	Coverage Δ
keras	82.63% <92.15%> (+0.01%)	⬆️
keras-jax	63.32% <0.00%> (-0.06%)	⬇️
keras-numpy	58.53% <0.00%> (-0.06%)	⬇️
keras-openvino	34.05% <92.15%> (+0.06%)	⬆️
keras-tensorflow	63.77% <0.00%> (-0.07%)	⬇️
keras-torch	63.44% <0.00%> (-0.06%)	⬇️

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[rkazants]

let us wait until slice_update tests are switched on

[Mohamed-Ashraf273]

@rkazants
I've switched on tests for slice_update.

[rkazants]

please add comments for each block

[Mohamed-Ashraf273]

@rkazants
I can't change it to opest15 because I'm facing a lot of segfaults when compiling models. I tried the version 2024.5.0 as mentioned here: https://docs.openvino.ai/2025/documentation/openvino-ir-format/operation-sets/available-opsets.html, but it didn't work either.
So I added comments.

[divyashreepathihalli]

/gemini review

[gemini-code-assist]

Code Review

This pull request implements the slice_update operation for the OpenVINO backend. The implementation generates indices for all elements in the updates tensor and uses scatter_nd_update to perform the update. The changes also enable the corresponding tests for this operation. The implementation assumes a static rank for the input tensors, and the index generation function could be refactored for better readability.