Implement DSMR Chain Functionality

[aaronbuchwald]

The chain type ties together the required functionality of building/parsing/executing/accepting blocks (as well as PreExecute for the mempool), which is used by the VM.

Implement the equivalent functionality for the DSMR package (excluding pre-execute since this will be handled at the mempool layer):

type Chain interface {
	// BuildBlock produces a new chunk based block skipping any duplicates that have either already been accepted
	// or are included in the processing ancestry of parent.
	BuildBlock(ctx context.Context, parent ExecutedBlock) (ExecutionBlock, error)
	// Execute executes the given block with the provided parent (guaranteed to have been executed successfully).
	// Execute verifies each chunk certificate as valid within the current epoch and 
	Execute(ctx context.Context, parentBlock ExecutedBlock, block ExecutionBlock) (ExecutedBlock, error)
	// ParseBlock returns an execution block that can be executed against its parent.
	ParseBlock(ctx context.Context, bytes []byte) (ExecutionBlock, error)
	// AcceptBlock accepts the given executed block, re-assembles the inner block, and executes the inner block.
	AcceptBlock(ctx context.Context, parent AcceptedBlock, block ExecutedBlock) (AcceptedBlock, error)
}