fix: Improve authentication handling in fetchWithAuth.

[anuragchvn-blip]

🚀 What This PR Does

• Improves fetchWithAuth by adding better error handling for getAccessToken().
• Logs meaningful errors when retrieving an access token fails.
• Ensures API calls in Supabase SDK always have proper authentication headers.

🔧 Why This Is Important

• Prevents silent failures in authentication.
• Improves debugging experience for developers using Supabase SDK.

✅ How to Test

1. Run Supabase SDK in a Node.js and browser environment.
2. Intentionally break getAccessToken() to verify error logging.

Would love feedback from maintainers! 🚀