format: add clang-format for sgl-kernel (#2483)

sgl-kernel/Makefile

@@ -1,4 +1,4 @@
-.PHONY: tree ln install build clean test
+.PHONY: tree ln install build clean test format
 
 tree:
 	@tree --prune -I "__pycache__|*.egg-info|*.so|build"
@@ -17,3 +17,6 @@ clean:
 
 test:
 	@pytest tests/
+
+format:
+	@find src tests -name '*.cc' -o -name '*.cu' -o -name '*.cuh' -o -name '*.h' | xargs clang-format -i && find src tests -name '*.py' | xargs isort && find src tests -name '*.py' | xargs black