Migration to Pydantic 2

[apirogov]

Pydantic 2 has many breaking changes, but migration to it might remove the need for much of the custom hacks that metador_core includes + increase speed. This will take some time and needs thinking through what must be touched.

• Remove custom decorator-based serializer system in favor of the new modular functional serialization
• Remove or adjust the custom parser system in favor of the new modular functional validators (question: would the Model to Model conversion work with that correctly?)
• Remove custom Strict aliases and use new strict mode by default (i.e. no number/bool coercion)

Lots of internal type-hint plumbing must be fixed, affecting

• dynamic creation of Partial Schemas (i.e. foundation of the harvesters), that must be re-engineered
• dynamic introspection of schemas (because model internals have been renamed or removed or refactored)
• custom metaclass magic (on which the whole schema system is based)

Furthermore, it might be time to

• remove the unused code of the custom and broken json schema generation and check out capabilities of the new default schema generation