Both `_input_callback` and `_async_input_callback` are added to `litellm.input_callback` (lines 334-337 in setup_once), but `_async_input_callback` simply calls `_input_callback` directly. If litellm invokes both callbacks for the same request, `_input_callback` will execute twice, creating duplicate spans for the same operation. This could lead to incorrect tracing data and span leaks since `span.__enter__()` is called multiple times but may not have matching `__exit__()` calls.

The PR adds `_async_input_callback` and `_async_success_callback` for async litellm operations but does not add a corresponding `_async_failure_callback`. If litellm invokes async callbacks for failure scenarios when using `acompletion()` or `aembedding()`, exceptions may not be properly captured and spans may not be closed. The existing tests `test_async_exception_handling` pass, suggesting the sync callback may still be called, but this creates an inconsistency in the callback registration pattern.