feat(db): Add Supabase client and database instances caching (#2513)

This pull request adds caching for the Supabase client and database
instances in order to improve performance and reduce unnecessary API
calls. The `get_supabase_client()` and `get_supabase_db()` functions now
check if the instances have already been created and return the cached
instances if available. This avoids creating new instances for every
function call, resulting in faster execution times.

backend/models/settings.py

@@ -1,3 +1,4 @@
+from typing import Optional
 from uuid import UUID
 
 from langchain.embeddings.ollama import OllamaEmbeddings
@@ -120,17 +121,26 @@ class ResendSettings(BaseSettings):
     resend_api_key: str = "null"
 
 
+# Global variables to store the Supabase client and database instances
+_supabase_client: Optional[Client] = None
+_supabase_db: Optional[SupabaseDB] = None
+
+
 def get_supabase_client() -> Client:
-    settings = BrainSettings()  # pyright: ignore reportPrivateUsage=none
-    supabase_client: Client = create_client(
-        settings.supabase_url, settings.supabase_service_key
-    )
-    return supabase_client
+    global _supabase_client
+    if _supabase_client is None:
+        settings = BrainSettings()  # pyright: ignore reportPrivateUsage=none
+        _supabase_client = create_client(
+            settings.supabase_url, settings.supabase_service_key
+        )
+    return _supabase_client
 
 
 def get_supabase_db() -> SupabaseDB:
-    supabase_client = get_supabase_client()
-    return SupabaseDB(supabase_client)
+    global _supabase_db
+    if _supabase_db is None:
+        _supabase_db = SupabaseDB(get_supabase_client())
+    return _supabase_db
 
 
 def get_embeddings():