rel_2_1_0b1

✨ New Features

• Free-threaded Python versions are now supported in wheels released on Pypi.
• The `_orm.relationship.back_populates` argument to `_orm.relationship()` may now be passed as a Python callable, which resolves to either the direct linked ORM attribute, or a string value as before.
• Added new hybrid method `hybrid_property.bulk_dml()` which works in a similar way as `hybrid_property.update_expression()` for bulk ORM operations.
• Added new parameter `_orm.composite.return_none_on` to `_orm.composite()`, which allows control over if and when this composite attribute should resolve to `None` when queried or retrieved from the object directly.
• Added support for per-session execution options that are merged into all queries executed within that session via the `_orm.Session.execution_options` parameter in session constructors.
• Session autoflush behavior has been simplified to unconditionally flush the session each time an execution takes place, regardless of whether an ORM statement or Core statement is being executed.
• Added `_orm.RegistryEvents` event class that allows event listeners to be established on a `_orm.registry` object, including `resolve_type_annotation()`, `before_configured()`, and `after_configured()` events.
• Added the utility method `_orm.Session.merge_all()` and `_orm.Session.delete_all()` that operate on a collection of instances.
• Added support for using `_orm.with_expression()` to populate a `_orm.query_expression()` attribute that is also configured as the `polymorphic_on` discriminator column.
• Added default implementations of `ColumnOperators.desc()`, `ColumnOperators.asc()`, `ColumnOperators.nulls_first()`, `ColumnOperators.nulls_last()` to `_orm.composite()` attributes, by default applying the modifier to all contained columns.