Nested tuple unpacking

WARNING - full AI-assisted solutions are not welcome for this issue The point of "Good first issues" is to give a chance to humans to interact and learn about the codebase. Writing code using AI assistant prevents this.

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This should work:

def main() -> None:
    tup = (1, (2, 3))
    a, (b, c) = tup
    print(a + b + c)

Currently it fails with AssertionError in the parser:

❯ spy /tmp/x.spy 
Traceback (most recent call last):
[...]
  File "/home/antocuni/anaconda/spy/spy/parser.py", line 544, in from_py_stmt_Assign
    assert isinstance(item, py_ast.Name)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError