feat: pydantic V2

[matthewelwell]

Update to pydantic V2. What I've done so far:

1. Updated the pydantic and pydantic-collections dependencies using pip-tools
2. pip install bump-pydantic && bump-pydantic flag_engine
3. Replaced the root_validator method _generate_default_composite_key on the IdentityModel with a computed_field named composite_key.
4. Added typeguard dependency and changed if isinstance(value, TRAIT_VALUE_TYPES) to check_type(value, TRAIT_VALUE_TYPES)

[github-actions[bot]]

File	Coverage
All files	100%	:white_check_mark:

Minimum allowed coverage is 100%

Generated by :monkey: cobertura-action against d02885eeea8655861b33337c848eb83c841ffb8b

[khvn26]

Finalised the work:

• Bumped pydantic to 2.2.1
• Bumped pydantic collections to 0.5.1
• Changed constrained type usage to annotated types
• Used computed_field for IdentityModel.composite_key
• Used correct model and field validators
• Used model_validate instead of parse_obj, model_dump instead if dict
• Acommodated for Pydantic V2 parsing str trait values to str
• Bumped engine version to 5.0.0

Switched typeguard usage to type_annotations.TypeGuard type instead.

[khvn26]

Closing in favour of https://github.com/Flagsmith/flagsmith-engine/pull/190 to allow @matthewelwell to review.