Create version 1 of Pydantic 2 breaking libs

[sinclert-canonical]

This PR creates version 1 of those libraries that would suffer breaking changes due to the support of Pydantic 2:

• data_models.
• upgrade.

Given that this is the first PR that bumps the major version of some of the libraries, some code shuffling was required to give the repository a cohesive view of what is still in v0, and what is available both in v0 and v1.

---

Pydantic 2 specific changes:

Pydantic 2 breaking changes can be seen in commit d08fbaa.

Code substitutions

- from pydantic import validator
+ from pydantic import field_validator

- from pydantic import root_validator
+ from pydantic import model_validator

- field.outer_type_
+ field.annotation

- obj.dict
+ obj.model_dump

- obj.__fields__
+ obj.model_fields

- type(self.dependency_model)(**json.loads(deps))
+ type(self.dependency_model).model_validate_json(deps)

- json.dumps(self.dependency_model.dict())
+ self.dependency_model.model_dump_json()

---

Code shuffling changes:

• Moved + adapted all previous integration tests into tests/v0/integration.
• Moved + adapted all previous unit tests into tests/v0/unit.
• Copied + adapted data_models.py and upgrade.py tests into tests/v1/unit.
• Copied + adapted data_models.py and upgrade.py libs into libs/charms/data_platform_libs/v1.
• Adapted Tox.ini environments to allow for -v0 and -v1 suffixes.
• Adapted CI workflow to use the new Tox environments.