### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

### Description

Starting in v1.83, all Langfuse success callbacks silently fail with an `AttributeError`. No traces are sent to Langfuse. The error is non-blocking so LLM calls still succeed, making this hard to detect without log monitoring.

### Version

- **Broken**: `v1.83.3-stable` (and likely all v1.83.x) - **Working**: `v1.81.12`

### Error

``` Langfuse Layer Error - Exception occurred while logging success event: 'NoneType' object has no attribute 'get'

Traceback (most recent call last): File "litellm/integrations/langfuse/langfuse_prompt_management.py", line 307, in async_log_success_event langfuse_logger_to_use = LangFuseHandler.get_langfuse_logger_for_request( globalLangfuseLogger=self, standard_callback_dynamic_params=standard_callback_dynamic_params, in_memory_dynamic_logger_cache=in_memory_dynamic_logger_cache, ) File "litellm/integrations/langfuse/langfuse_handler.py", line 40, in get_langfuse_logger_for_request LangFuseHandler._dynamic_langfuse_credentials_are_passed( standard_c…