feat: support for google genai module via new llms/googleai/googlegenai module

[jackmcguire1]

Description

This PR adds a new module under llms/googleai, similar to vertex to export a new GoogleAi interface that interacts via the new "google.golang.org/genai" explicitly

https://github.com/tmc/langchaingo/issues/1120

• support for "google.golang.org/genai" module that supports both vertex and gemini

• support for embedding not implemented

• [X] Read the Contributing documentation.

• [X] Read the Code of conduct documentation.

• [X] Contains test coverage for new functions.

[tmc]

Thanks for the contribution @jackmcguire1 -- can we reduce this PR to not change deps that don't need updating and pull the go version bump. If anything I'd like to change the project to be as expansive as possible wrt go versions.

[olegsu]

Hey, is there a plan to merge this eventually? Google deprecated the google/generative-ai-go back in March and it will stop receive updates by the end of September.

[uppercaveman]

Has this plan been forgotten?