Try constructor improvements for Delegations/ delegated roles

Currently creating e.g. succinct delegations looks like this

BIT_LENGTH = int(math.log2(NUMBER_OF_BINS))
succinct_roles = SuccinctRoles(
    keyids=[bins_key.keyid],
    threshold=THRESHOLD,
    bit_length=BIT_LENGTH,
    name_prefix=NAME_PREFIX,
)
delegations_keys_info: Dict[str, Key] = {}
delegations_keys_info[bins_key.keyid] = bins_key

targets.signed.delegations = Delegations(
    delegations_keys_info, roles=None, succinct_roles=succinct_roles
)

Looks bad, i'm sure we could get that to something a bit like:

targets.signed.delegations = Delegations(SuccinctRoles.new(NUMBER_OF_BINS, NAME_PREFIX))
targets.add_key(bins_key)

Or alternatively

targets.signed.delegations = Delegations.new_succint(NUMBER_OF_BINS, NAME_PREFIX)
targets.add_key(bins_key)

What makes sense probably depends on what the other delegation types (most importantly paths delegation) will look like...

Beginne damit, die Konstruktoren von Delegations und SuccinctRoles zu lesen, und vergleiche sie dann mit den anderen Delegationstypen, insbesondere mit Pfaddelegationen. Das Design ist abgeschlossen, wenn das Projekt einen vereinbarten einfacheren Konstruktionsablauf für Succinct-Delegationen und die Schlüsselregistrierung hat, der zu den anderen Delegation-APIs passt.