fix: close WSGI response iterables after consumption

[Shubham Padkonde (Shubham-Padkonde)]

The WSGI adapter consumes the application's response iterable without calling its close() method. File responses can consequently leave their streams open, and framework cleanup callbacks are skipped.

Close the original response iterable in a finally block after consuming it, as required by PEP 3333. This also releases resources when iteration raises, while preserving the original iteration error when cleanup succeeds. Iterables without close() continue to work.

Validation: 890 tests pass and two are skipped on Python 3.13. New regressions cover a real Werkzeug file wrapper, an empty response, and an iteration error; all three fail before the fix. Flake8 E/F/W checks pass. The docstring plugin reports the same two pre-existing findings on the original and modified WSGI module.

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