chore: type constructor_eager as ConstructorEager instead of Constructor

[MarcoGorelli]

In here

narwhals/tests/utils.py

Line 20 in 9353ef9

Constructor: TypeAlias = Callable[[Any], IntoFrame]

we have Constructor

The task is here it to:

• make ConstructorEager, with IntoDataFrame instead of IntoFrame
• in tests that have constructor_eager: Any, use instead constructor_eager: ConstructorEager. You may need to import it, see other tests for examples

[lucianosrp]

I'll take this one if no one is on it 😊