Bug: Attribute completion broken for line magics with multiple arguments

Bug: Attribute completion broken for line magics with multiple arguments: a task in LegoFlow-SWE (Harbor dataset). When using tab completion with line magics that take multiple arguments, attribute completion fails completely. For example, %timeit -n 2 -r 1 os.<tab does not show any completions…

The task

When using tab completion with line magics that take multiple arguments, attribute completion fails completely. For example, `%timeit -n 2 -r 1 os.<tab>` does not show any completions, even though `os.<tab>` alone works.

Part of Lego-X/LegoFlow-SWE.