Remove type attributes

[sanmai]

As per #379 (comment)

To be clear, I would seriously love to see a next major version with type annotations. But if there's a choice between getting a minor version bump and no release, I'd prefer to have the release pipeline going. If this makes any sense.

Please feel free to close this PR if you'd rather stick with typed properties.

[michelf]

I think per the versioning policy we should keep the types attributes for protected properties.

For the public ones, this is more nuanced, and I'm still trying to wrap my head around it. Strictly speaking this is a breaking change for users using declare(strict_types=1). Even without this mode, it could in some case create errors where a user of the library would be setting a string property with an array value, or the reverse (which might or might not create an error down the line depending on the parsed input). In practice I doubt very much it'd affect anyone. It all seems very unlikely to me, but I don't really know. Any comment on that?

In any case I don't think the downsides of making it a major version (slowing down adoption, prompting people to read a changelog saying "we added type attributes" before deciding to allow a 2.0.0 version) is worth it.

[sanmai]

Sounds great to me! Following this with #383