fix(sqla_factory): added an async context manager in SQLAASyncPersistence

[nisemenov]

Description

• an async context manager has been added in SQLAASyncPersistence class to prevent

...
raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

The garbage collector is trying to clean up non-checked-in connection <AdaptedConnection <asyncpg.connection.Connection
object>>, which will be terminated.  Please ensure that SQLAlchemy pooled connections are returned to the pool 
explicitly, either by calling ``close()`` or by using appropriate context managers to manage their lifecycle.

sys:1: SAWarning: The garbage collector is trying to clean up non-checked-in connection <AdaptedConnection 
<asyncpg.connection.Connection object>>, which will be terminated.  Please ensure that SQLAlchemy pooled connections are 
returned to the pool explicitly, either by calling ``close()`` or by using appropriate context managers to manage 
their lifecycle.

Closes

• Closes feat(sqla_factory): added __set_association_proxy__ attribute #624

[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/polyfactory-docs-preview/630