Perf: Increase database connection pool size (#7559)

### What problem does this PR solve?

1. The MySQL instance is configured with max_connections=1000,
but our connection pool was limited to max_connections: 100.
This mismatch caused connection pool exhaustion during performance
testing.

2.  Increase stale_timeout to resolve #6548

### Type of change

- [x] Performance Improvement

api/db/services/llm_service.py

@@ -105,7 +105,7 @@ class TenantLLMService(CommonService):
         if model_config:
             model_config = model_config.to_dict()
             llm = LLMService.query(llm_name=mdlnm) if not fid else LLMService.query(llm_name=mdlnm, fid=fid)
-            if not llm and fid: # for some cases seems fid mismatch
+            if not llm and fid:  # for some cases seems fid mismatch
                 llm = LLMService.query(llm_name=mdlnm)
             if llm:
                 model_config["is_tools"] = llm[0].is_tools
@@ -163,12 +163,6 @@ class TenantLLMService(CommonService):
     @classmethod
     @DB.connection_context()
     def increase_usage(cls, tenant_id, llm_type, used_tokens, llm_name=None):
-        try:
-            if not DB.is_connection_usable():
-                DB.connect()
-        except Exception:
-            DB.close()
-            DB.connect()
         e, tenant = TenantService.get_by_id(tenant_id)
         if not e:
             logging.error(f"Tenant not found: {tenant_id}")
@@ -366,7 +360,7 @@ class LLMBundle:
 
         ans = ""
         chat_streamly = self.mdl.chat_streamly
-        total_tokens = 0 
+        total_tokens = 0
         if self.is_tools and self.mdl.is_tools:
             chat_streamly = self.mdl.chat_streamly_with_tools