chore: add native return types

[DevinCodes]

Q	A
Bug fix?	no
New feature?	no
BC breaks?	yes

Describe your change

This adds native return types to some methods to prevent Symfony from raising deprecation warnings.

[DevinCodes]

I had to revert the changes made in #364, as it turns out the change wouldn't work for Symfony v6: the definition for Symfony's NormalizableInterface is not backwards compatible with older PHP versions, meaning that we need to introduce a new major version in order to add support for symfony v6 and up. This would break compatibility for older versions. cc @damcou

[Bukashk0zzz]

Any news? This PR will allow us to upgrade to Symfony 6. I think a lot of people have the same issue.
From what I see in other repositories, there is no other way than introduce a new major version with ^5.4|^6.0 support only.

[DevinCodes]

I'll bring this up during our upcoming team discussions, and keep you posted on the outcome 🙂

[Kaaly]

Some news on this PR ?

[barrycarton]

I'll bring this up during our upcoming team discussions, and keep you posted on the outcome 🙂

Hey @DevinCodes could you give us a rough estimate on the ETA since the patch is ready. Feel free to ask if you want some help.

[DevinCodes]

Hi all! We'll need to release a new major that only supports modern versions of Symfony. I'll prepare the release for this tomorrow, and I'll try to get it out before the weekend!

[damcou]

Looks good :)

[DevinCodes]

Merging this and releasing tomorrow!