feat: Use Sequence instead of list in type hints

[kylebarron]

This is a good quick note on variance in Python and this is a good resource on variance of list vs Sequence:

Key Terms

1. Covariant: If A is a subtype of B, then Container[A] is a subtype of Container[B].
2. Contravariant: If A is a subtype of B, then Container[B] is a subtype of Container[A].
3. Invariant: Neither covariant nor contravariant. Container[A] and Container[B] are not related, even if A and B are.

list is invariant while Sequence is covariant.

We want our type hints to be covariant so that users can return a subtype of ObjectMeta.