Add support for wsgi.file_wrapper

[dalf]

I've tried to run https://github.com/benbusby/whoogle-search a WSGI application using granian --interface wsgi app.

The logs show that wsgi.file_wrapper is not supported:

[ERROR] Exception on /static/build/main.68be5054.css [GET]
Traceback (most recent call last):
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/flask/app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/flask/app.py", line 1951, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/flask/app.py", line 1820, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/flask/app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/flask/app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/flask/helpers.py", line 1081, in send_static_file
    return send_from_directory(
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/flask/helpers.py", line 771, in send_from_directory
    return send_file(filename, **options)
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/flask/helpers.py", line 640, in send_file
    data = wrap_file(request.environ, file)
  File "/home/alexandre/code/whoogle-search/venv/lib/python3.9/site-packages/werkzeug/wsgi.py", line 529, in wrap_file
    return environ.get("wsgi.file_wrapper", FileWrapper)(file, buffer_size)
TypeError: 'NoneType' object is not callable

For reference: https://peps.python.org/pep-3333/#optional-platform-specific-file-handling

[gi0baro]

@dalf so, aside from supporting this, since is optional, this is actually a bug, as Granian should not populate the wsgi.file_wrapper key of environ.

I gonna leave this opened for the support request, while the bug is now tracked in #41. Once closed, the app you tried should work without the file wrapper support.

[gi0baro]

I'm closing this as wsgi.file_wrapper is implemented around file descriptors, so it won't be beneficial in the same way of ASGI zerocopysend in #93