Parser Idempotency: Generator drops indentation on nested def

[addisoncrump]

The following source code is incorrectly round-tripped by ruff_python_ast::source_code::round_trip:

def d():
    def e():
        pass

The result is:

def d():

    
def e():
        pass

Which is invalid syntax.

This error does not seem to persist to the Ruff command line. The cause appears to be that newlines are explicitly invoked for def and some other types, but the indent is not applied afterward. This appears to affect all types of def in unparse_stmt, so I'm not quite sure how this isn't propagating to frontend.

Discovered by #4822