Marshmallow

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Features:

- Add ``many`` Meta option to ``Schema`` so it expects a collection by default (:issue:`2270`).
Thanks :user:`himalczyk` for reporting and :user:`deckar01` for the PR.
- Refactor hooks (:pr:`2279`).
Thanks :user:`deckar01` for the PR.

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Bug fixes:

- Fix memory leak that prevented schema instances from getting GC'd (:pr:`2277`).
Thanks :user:`mrcljx` for the PR.

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Bug fixes:

- Allow timestamp 0 in ``fields.DateTime`` (:issue:`2133`).
Thanks :user:`flydzen` for reporting.

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Bug fixes:

- Fix error message when field is declared as a class and not an instance (:issue:`2245`).
Thanks :user:`travnick` for reporting.

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Bug fixes:

- Fix validation of ``URL`` fields to allow missing user field,
per NWG RFC 3986 (:issue:`2232`). Thanks :user:`ddennerline3` for reporting
and :user:`deckar01` for the PR.

Other changes:

- *Backwards-incompatible*: ``__version__``, ``__parsed_version__``, and ``__version_info__``
attributes are deprecated (:issue:`2227`). Use feature detection or
``importlib.metadata.version("marshmallow")`` instead.

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Bug fixes:

- Fix ``Nested`` field type hint for lambda ``Schema`` types (:pr:`2164`).
Thanks :user:`somethingnew2-0` for the PR.

Other changes:

- Officially support Python 3.12 (:pr:`2188`).
Thanks :user:`hugovk` for the PR.