fix!: fix auth_methods module

[twishabansal]

This PR fixes the get_google_id_token and aget_google_id_token methods to get google id token from google cloud environments.

This code has been manually tested for the following cases:

• Toolbox server is deployed on Cloud Run but the application is running locally.
• Both the Toolbox server and the application and deployed on Cloud Run.

Fixes googleapis/genai-toolbox#806, #311, #310

For personal accounts on local environments, users can keep using the existing code.
For other cases,

Before:

from toolbox_core import ToolboxClient, auth_methods

# Replace with the Cloud Run service URL generated in the previous step.
URL = "https://cloud-run-url.app"

auth_token_provider = auth_methods.aget_google_id_token # can also use sync method

async with ToolboxClient(
    URL,
    client_headers={"Authorization": auth_token_provider},
) as toolbox:
   # use as needed

After

from toolbox_core import ToolboxClient, auth_methods

# Replace with the Cloud Run service URL generated in the previous step.
URL = "https://cloud-run-url.app"

auth_token_provider = auth_methods.aget_google_id_token(URL) # can also use sync method

async with ToolboxClient(
    URL,
    client_headers={"Authorization": auth_token_provider},
) as toolbox:
   # use as needed