Use compact blinded paths for short-lived offers

Use compact blinded paths for short-lived offers

When an offer is short-lived, the likelihood of a channel used in a
compact blinded path going away is low. Require passing the absolute
expiry of an offer to ChannelManager::create_offer_builder so that it
can be used to determine whether or not compact blinded path should be
used.

Use the same criteria for creating blinded paths for refunds as well.