fix(backend): handle async functions in AST parsing utilities

[harshhh817]

What this does

Treats ast.AsyncFunctionDef the same as ast.FunctionDef in kale/common/astutils.py, so async def helpers in a functions/step cell are handled correctly by:

• parse_functions — now extracts async functions (previously dropped them).
• get_function_and_class_names — now registers async function names.
• get_marshal_candidates — now stops at async function bodies, so it no longer leaks their local variables and correctly adds the function name.

Why

astutils only checked ast.FunctionDef, so an async def was mishandled in three ways. Reproducer on main:

from kale.common import astutils

astutils.parse_functions("async def foo():\n    return 1")
# {}                      -> expected {"foo": ...}

astutils.get_function_and_class_names("async def foo():\n    pass")
# set()                   -> expected {"foo"}

astutils.get_marshal_candidates("async def foo():\n    local_x = 1\n    return local_x")
# ['local_x']             -> expected ['foo']

The get_marshal_candidates case is the most harmful: it walked into the async function body and returned the function's local variable as a marshal candidate while missing the function name. In a pipeline this means an async def helper would not be injected into steps, would be treated as a missing dependency, and its internals could be marshalled between steps.

Testing

Extended kale/tests/unit_tests/test_ast.py with an async snippet and a dedicated parse_functions async test. All three new assertions fail on main and pass with this change; the full test_ast.py suite (47 tests) passes.

I came across this while working on the output-artifact/AST code in #874. Happy to open a tracking issue if maintainers prefer.

[google-oss-prow]

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[harshhh817]

Friendly ping — small backend fix: astutils only checked ast.FunctionDef, so an async def helper was dropped by parse_functions, its name was missing from get_function_and_class_names, and get_marshal_candidates walked into its body and returned the function's local variables as marshal candidates.

Regression tests included; still green. Happy to rebase onto current main if that helps.