Use google.golang.org/genai

[jackmcguire1]

Background

Google has released a new central package for genai

Please update the llms/googleai files to

• remove references to github.com/google/generative-ai-go/genai

• Instead use google.golang.org/genai

Notes

• This should be somewhat interchangeable

• might need to adapt the support for selecting Vertex or Gemini API

• This package also now supports for live multi-modal so we could extend module capabilities further