Fixed issue #17671 by adding the required decorators

[Riddhimaan-Senapati]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes #17671

The .achat and .acomplete method in the Gemini client (/llama-index-integrations/llms/llama-index-llms-gemini/llama_index/llms/gemini/base.py) do not have the @llm_completion_callback() and @llm_chat_callback() decorators. So I added them. This should solve issue #17671

New Package?

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• No

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Your pull-request will likely not be merged unless it is covered by some form of impactful unit testing.

• I added new unit tests to cover this change
• I believe this change is already covered by existing unit tests

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran make format; make lint to appease the lint gods

[Riddhimaan-Senapati]

@logan-markewich @tobi @wpiekutowski @xevo @bborn Can anyone of you review my PR?