feat: add Attribute base class for custom model casts and sqlite cast tests

[tmgbedu]

Summary

• Add Attribute(BaseModel) to caster.py — a reusable mixin that turns any Pydantic model into a custom ORM cast. Subclasses get JSON serialization/deserialization for free via get/set classmethods backed by model_dump_json
• Export Attribute from fastapi_startkit.masoniteorm so users can import it directly
• Fix get_attributes_for_insert to apply set casts to _attributes, allowing Address instances and dicts to be passed directly to create() without manual JSON serialization
• Add preferences (dict/list) and address (Attribute subclass) columns to the users fixture table with seeder and model updates
• Add test_sqlite_model_casts.py with 11 tests covering int, str, bool, dict, list, and custom Pydantic Attribute casts — including insert with an instance and a dict

Usage

from fastapi_startkit.masoniteorm import Attribute

class Address(Attribute):
    street: Optional[str] = None
    city: Optional[str] = None

class User(Model):
    address: Address  # wired up automatically

# All three forms work on insert
await User.create({"address": Address(street="123 Main St", city="Sydney")})
await User.create({"address": {"street": "123 Main St", "city": "Sydney"}})

Test plan

• All 11 tests in test_sqlite_model_casts.py pass
• Existing sqlite test suite unaffected

🤖 Generated with Claude Code