manifest: introduce a `read_delta_parents` method
This new method have a clearer semantic and can be used by code that need this
semantic. This should avoid bugs, allow for more targeted optimisation, and
provide a clearer API. Users will be updated in subsequent changesets.
This is also part of the wider effort to clarify and fix this API. one more
method coming.
import hashlib
try:
from ..thirdparty import sha1dc # pytype: disable=import-error
sha1 = sha1dc.sha1
except (ImportError, AttributeError):
sha1 = hashlib.sha1