Shorter success callbacks from /health/readiness

Before:

```shell
$ curl -sSL http://0.0.0.0:4000/health/readiness | jq '.success_callbacks'
[
  "langfuse",
  "<function _PROXY_track_cost_callback at 0x12fc14b80>",
  "<bound method SlackAlerting.response_taking_too_long_callback of <litellm.integrations.slack_alerting.SlackAlerting object at 0x12cedb740>>",
  "<litellm.proxy.hooks.parallel_request_limiter._PROXY_MaxParallelRequestsHandler object at 0x12cedb8f0>",
  "<litellm.proxy.hooks.max_budget_limiter._PROXY_MaxBudgetLimiter object at 0x12cedb830>",
  "<litellm.proxy.hooks.cache_control_check._PROXY_CacheControlCheck object at 0x12ca101d0>",
  "<litellm._service_logger.ServiceLogging object at 0x13a6d8c50>"
]
```

After:

```shell
$ curl -sSL http://0.0.0.0:4000/health/readiness | jq '.success_callbacks'
[
  "langfuse",
  "_PROXY_track_cost_callback",
  "response_taking_too_long_callback",
  "_PROXY_MaxParallelRequestsHandler",
  "_PROXY_MaxBudgetLimiter",
  "_PROXY_CacheControlCheck",
  "ServiceLogging"
]
```

litellm/proxy/health_endpoints/_health_endpoints.py

@@ -406,6 +406,19 @@ async def active_callbacks():
     }
 
 
+def callback_name(callback):
+    if isinstance(callback, str):
+        return callback
+
+    try:
+        return callback.__name__
+    except AttributeError:
+        try:
+            return callback.__class__.__name__
+        except AttributeError:
+            return str(callback)
+
+
 @router.get(
     "/health/readiness",
     tags=["health"],
@@ -424,8 +437,8 @@ async def health_readiness():
         try:
             # this was returning a JSON of the values in some of the callbacks
             # all we need is the callback name, hence we do str(callback)
-            success_callback_names = [str(x) for x in litellm.success_callback]
-        except:
+            success_callback_names = [callback_name(x) for x in litellm.success_callback]
+        except AttributeError:
             # don't let this block the /health/readiness response, if we can't convert to str -> return litellm.success_callback
             success_callback_names = litellm.success_callback