Itemadapter

Dropped Python 3.6 support, and made Python 3.11 support official
([65](https://github.com/scrapy/itemadapter/pull/65),
[66](https://github.com/scrapy/itemadapter/pull/66),
[69](https://github.com/scrapy/itemadapter/pull/69)).

It is now possible to declare custom `ItemAdapter` subclasses with their own
`ADAPTER_CLASSES` attribute, allowing to support different item types in
different parts of the same code base
([68](https://github.com/scrapy/itemadapter/pull/68)).

Improved type hint support
([67](https://github.com/scrapy/itemadapter/pull/67)).

ItemAdapter.get_field_names_from_class
([64](https://github.com/scrapy/itemadapter/pull/64))

Slight performance improvement
([62](https://github.com/scrapy/itemadapter/pull/62))

Improve performance by removing imports inside functions
([60](https://github.com/scrapy/itemadapter/pull/60))

Added `ItemAdapter.is_item_class` and `ItemAdapter.get_field_meta_from_class`
([54](https://github.com/scrapy/itemadapter/pull/54))

Added built-in support for `pydantic` models ([53](https://github.com/scrapy/itemadapter/pull/53))