hotfix: add CustomOp abstraction

[zhyncs]

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Motivation

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Modification

Briefly describe the changes made in this PR.

Checklist

1. Ensure pre-commit pre-commit run --all-files or other linting tools are used to fix potential lint issues.
2. Confirm that modifications are covered by complete unit tests. If not, please add more unit tests for correctness.
3. Modify documentation as needed, such as docstrings or example tutorials.

[merrymercy]

We also need to update here

sglang/python/sglang/srt/model_executor/cuda_graph_runner.py

Line 43 in 33d6135

if isinstance(sub, CustomOp):