* fix: add __iter__ and __next__ to FileWrapper for PEP 3333 compliance
The WSGI spec (PEP 3333) requires that wsgi.file_wrapper return an
iterable object. Gunicorn's FileWrapper only implemented __getitem__,
which technically makes it iterable via old-style iteration but breaks
code that explicitly relies on the iterator protocol (e.g., calling
iter() or using next()).
This adds __iter__ (returning self) and __next__ to make FileWrapper
a proper iterator, maintaining backward compatibility with existing
__getitem__-based usage.
Fixes#3396
* Fix lint: move imports to top of file
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Co-authored-by: contributor <noreply@users.noreply.github.com>
Co-authored-by: Benoit Chesneau <bchesneau@gmail.com>
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