Add VM.create_genesis_header

The genesis header now needs to be VM-aware, to handle EIP-1559. Rather
than pass in a parent of None, it looks a bit cleaner to use the new
create_genesis_header.

Update an old create_header_from_parent usage to create_genesis_header.

Author: carver

eth/abc.py

@@ -3316,6 +3316,16 @@ def generate_block_from_parent_header_and_coinbase(cls,
         """
         ...
 
+    @classmethod
+    @abstractmethod
+    def create_genesis_header(cls, **genesis_params: Any) -> BlockHeaderAPI:
+        """
+        Create a genesis header using this VM's rules.
+
+        This is currently equivalent to create_header_from_parent(None, **genesis_params)
+        """
+        ...
+
     @classmethod
     @abstractmethod
     def get_block_class(cls) -> Type[BlockAPI]:

eth/chains/base.py

@@ -250,7 +250,7 @@ def from_genesis(cls,
                 f"Expected {genesis_params['state_root']!r}"
             )
 
-        genesis_header = genesis_vm_class.create_header_from_parent(None, **genesis_params)
+        genesis_header = genesis_vm_class.create_genesis_header(**genesis_params)
         return cls.from_genesis_header(base_db, genesis_header)
 
     @classmethod

eth/vm/base.py

@@ -443,6 +443,11 @@ def generate_block_from_parent_header_and_coinbase(cls,
         )
         return block
 
+    @classmethod
+    def create_genesis_header(cls, **genesis_params) -> BlockHeaderAPI:
+        # Create genesis header by setting the parent to None
+        return cls.create_header_from_parent(None, **genesis_params)
+
     @classmethod
     def get_block_class(cls) -> Type[BlockAPI]:
         if cls.block_class is None: