Update to pydantic v2

[CasperWA]

Use new way of configuring models and new type of validators.

Closes #12

I put this as a draft for now, to determine whether other parts of the code should be re-written according to new pydantic v2 functionality. Like, e.g., the dynamic model creation using create_model().

Furthermore, since dependencies of this package pin pydantic to v1 still, it is difficult to see an update happening right now.

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~This PR now does a few things, along with migrating to pydantic v2~ (EDIT: Nope, it just migrates):

• Use ruff instead of pylint and isort (this is also implemented in #19, so I advice to merge that one first and fix this afterwards). EDIT: This has been done.
• Update type annotations throughout the code base to be Python 3.10 styling (utilizing from __future__ import annotations, which should be removed once the minimum required Python version is set to 3.10). EDIT: This has been reverted - it doesn't work. Since Python 3.9 is the minimum supported version, Python 3.9 style typing has been implemented everywhere. Note, this can also be done dynamically using the pyupgrade package with the --py39-plus option (for example as a pre-commit hook, if so desired).

[CasperWA]

@quaat and @Treesarj, I think I'll merge this. It shouldn't change any contents, really, just update usage of pydantic to pydantic v2 styling - and then there's a bit of static typing updates as well.

Since both oteapi-core and otelib now support pydantic v2, there are no dependency issues any longer.