package_managers: generic: Use a serializer for URL-typed fields

[eskultety]

Pydantic formats down URL types as "type casts" in the serialized dictionary [1]. Apparently, that's by design and the docs advises to use custom serializers for given fields [2].

This patch is necessary, because pydantic 2.10.2 changed their behavior when it comes to handling URL types [3] and so once we bump the version we'd hit a test failure requiring us to change the unit test to "cast" some fields as AnyUrl rather than Url. Since these have no place in plain dictionaries, this patch fixes the problem in the correct way by the use of pydantic serializers.

[1] pydantic/pydantic#10998
[2] https://docs.pydantic.dev/latest/api/functional_serializers/#pydantic.functional_serializers.PlainSerializer
[3] https://pydantic.dev/articles/pydantic-v2-10-release#migrate-to-subclassing-instead-of-annotated-approach-for-pydantic-url-types

This relates to the changes necessary in order to eventually merge #756 .

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[slimreaper35]

https://github.com/pydantic/pydantic-core

NOTE: You should not need to use pydantic-core directly; instead, use pydantic, which in turn uses pydantic-core.

:) This looked suspicious to me. We have a couple of other imports, so we should fix them too.

[eskultety]

ACK, but that's a material for a standalone PR I believe, this one is purely targeting a fix allowing us to in turn bump the pydantic version updates more seamlessly.