Update for Gen AI SDK

[takumiohym]

Goal of this update:

• Merge dedicated kernels below into the main environment:
  • gemini_kernel
  • langchain_components_kernel
  • langchain_kernel
• Update Gemini API calls to use the new Gen AI SDK.

Tasks:

• Merge dependencies of 3 dedicated kernels into main requirements.
• Remove the kernel bash files and update related notebooks if necessary.
  • gemini_kernel Remove gemini kernel #564
  • langchain_components_kernel Remove langchain_kernel & update langchain to v0.3 #567
  • langchain_kernel Remove langchain_component_kernel & update langchain to v0.3 #568
• Update notebooks under vertex_genai to use Gen AI SDK
• Test notebooks that uses other updated dependencies (e.g. google-cloud-aiplatform)

[takumiohym]

Notes on requirements.txt update

• Merged 3 kernels and categorized/reordered
• Updated langchain libraries to v0.3.
• Added google-genai with the latest version as of 2025/12/16. Will update it later depending on the timing to merge the PR.
• Added some underlying dependency versions explicitly (e.g. kubernetes, jax, google-api-core, google-cloud-storage) to speed up the installation process by removing the necessity to install multiple versions and check compatibilities.
• Moved saliency to from the requirements-without-deps.txt to requirements.txt, as its dependencies don't crush with other libraries.