bug: get-by-id field raises KeyError when id_field_name differs from the primary key attribute #413

Description

A single-type root field built by strawchemy.field() exposes its primary key argument under id_field_name (config.default_id_field_name, or the field's own id_field_name), but the repository looks the value up under the primary key attribute name.

• src/strawchemy/schema/field.py (auto_arguments): for a single primary key, the argument is StrawberryArgument(self.id_field_name, ...).
• src/strawchemy/repository/sqlalchemy/_async.py (get_one/by-id lookup) and its _sync.py counterpart: kwargs.pop(field_def.name), where field_def.name is the mapper's primary key attribute.

When the two names differ, the lookup raises KeyError.

Reproduction

strawchemy = Strawchemy(StrawchemyConfig("postgresql", default_id_field_name="pk"))

@strawchemy.type(Fruit, include="all")
class FruitType: ...

@strawberry.type
class Query:
    fruit: FruitType = strawchemy.field()

{ fruit(pk: 1) { name } } fails with KeyError: 'id'.

tests/unit/schemas/custom_id_field_name.py only snapshots the schema, so no test executes this path. Composite primary keys are unaffected: their arguments use the attribute names.