Add type annotation for allzweckmesser.scan.scan

from typing import List

from .meters import ALL_METERS

from .model import Verse

from .scanner import Scanner

def scan(plain_verses: List[str], meters=ALL_METERS, **options):

def scan(plain_verses: List[str], meters=ALL_METERS, **options) -> List[Verse]:

    """Scan Latin verses."""

    scanner = Scanner()

    scanned_verses = scanner.scan_verses(plain_verses)