### What this PR does / why we need it?
Introduces the `acl_graph_print` function to enable printing debug
information from code running inside an ACL graph, such as custom
operators.
This works by launching a host function on a dedicated stream, bypassing
the limitations of standard `print` within compiled graph execution. The
implementation handles the necessary stream subscriptions and ensures
they are properly unregistered upon exit.
### Does this PR introduce _any_ user-facing change?
None.
### How was this patch tested?
None.
- vLLM version: v0.11.0
- vLLM main:
2918c1b49c
Signed-off-by: Yizhou Liu <liu_yizhou@outlook.com>
094f32c8c9