[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 90.47619% with 4 lines in your changes missing coverage. Please review.

Project coverage is 82.73%. Comparing base (d16424e) to head (a4188f1).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
keras/src/backend/openvino/core.py	90.47%	1 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21362      +/-   ##
==========================================
- Coverage   82.73%   82.73%   -0.01%     
==========================================
  Files         565      565              
  Lines       55215    55264      +49     
  Branches     8606     8617      +11     
==========================================
+ Hits        45682    45722      +40     
- Misses       7424     7429       +5     
- Partials     2109     2113       +4     

Flag	Coverage Δ
keras	82.54% <90.47%> (-0.01%)	⬇️
keras-jax	63.28% <0.00%> (-0.06%)	⬇️
keras-numpy	58.48% <0.00%> (-0.05%)	⬇️
keras-openvino	33.84% <90.47%> (+0.04%)	⬆️
keras-tensorflow	63.69% <0.00%> (-0.06%)	⬇️
keras-torch	63.32% <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.