bug: not able to call get_type_hints on *Node types

[ClementWalter]

See this MWE

from typing import get_type_hints
from ethereum.cancun.trie import BranchNode

get_type_hints(BranchNode)

This raises because the nodes use rlp.Extended as a type annotation instead of Extended.

Doing in rlp.py

from ..rlp import Extended

# ...

@slotted_freezable
@dataclass
class LeafNode:
    """Leaf node in the Merkle Trie"""

    rest_of_key: Bytes
    value: Extended


@slotted_freezable
@dataclass
class ExtensionNode:
    """Extension node in the Merkle Trie"""

    key_segment: Bytes
    subnode: Extended


@slotted_freezable
@dataclass
class BranchNode:
    """Branch node in the Merkle Trie"""

    subnodes: List[Extended]
    value: Extended

solves the issue.