Partial callback support

[Gallaecio]

I’m told scrapy-poet, specifically the downloader middleware, triggers and exception when using scrapy-inline-requests due to not supporting functools.partial callbacks:

File "/app/python/lib/python3.11/site-packages/scrapy_poet/[injection.py](https://injection.py/)", line 467, in is_callback_requiring_scrapy_response
    callback_type_hints = get_type_hints(callback)
  File "/usr/local/lib/python3.11/[typing.py](https://typing.py/)", line 2359, in get_type_hints
    raise TypeError('{!r} is not a module, class, method, '

While I don’t think we need to support scrapy-inline-requests given modern Scrapy has built-in support for inline requests, supporting partial callbacks may be useful for other scenarios.