Fix WrongType for UIDReferenceField

[nnpvaan]

Description of the issue/feature this PR addresses

Fix WrongType errors when setting DX UIDReferenceField values via JSONAPI push, e.g. for IClientShareableBehavior.clients, by normalizing collected UIDs to native strings before field validation.

Current behavior before PR

Creating or updating objects through JSONAPI push that include UIDReferenceField values (notably IClientShareableBehavior.clients) fails with an error similar to:

Cannot create object: TypeError - WrongType: Field=senaite.core.behaviors.clientshareable.IClientShareableBehavior.clients Value=[u'...']

because the underlying List(ASCIILine) receives a list of Unicode UIDs instead of native str, causing WrongType/WrongContainedType during validation.

Desired behavior after PR is merged

UID reference field manager normalizes all collected references to native str UIDs before calling the field’s setter, so creating/updating objects with UIDReferenceField values (including clients) via JSONAPI succeeds and relations/backrefs are stored correctly, without raising WrongType errors.

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I confirm I have tested the PR thoroughly and coded it according to PEP8
standards.

[xispa]

Thanks!