fix: Support SQLAlchemy inheritance patterns

[cofin]

Fixes automatic table name generation to support SQLAlchemy's inheritance patterns.

Changes

Implements detection and handling for:

• Single Table Inheritance (STI) - child classes automatically use parent's table
• Joined Table Inheritance (JTI) - separate tables with foreign key relationship
• Concrete Table Inheritance (CTI) - independent tables with concrete=True

Implementation

• Uses has_inherited_table() to detect STI pattern and return None for child tablenames
• Adds __table_cls__ hook to inspect columns and prevent duplicate table creation
• Updates __init_subclass__ to set tablename=None for STI children before SQLAlchemy processes class
• Handles edge cases: explicit tablenames, multi-level inheritance, mixins, abstract bases

Example

class Employee(UUIDBase):
    __tablename__ = "employee"
    type: Mapped[str]
    __mapper_args__ = {
        "polymorphic_on": "type",
        "polymorphic_identity": "employee"
    }

# STI - automatically uses parent table
class Manager(Employee):
    __mapper_args__ = {"polymorphic_identity": "manager"}
    department: Mapped[str | None] = mapped_column(default=None)

[cofin]

Superseded by PR #611 which provides a complete implementation with comprehensive test coverage and support for all inheritance patterns (STI, JTI, CTI).