localrepo: introduce a `_quick_access_changeid` property Having faster access to `null` is cute… but limited. We want to speedup access to more useful revision, like `.`. We start with turning the fast path for `null` into something more generic. Differential Revision: https://phab.mercurial-scm.org/D7488

changectx: use unfiltered changelog to access parents of unfiltered revs If a revision is not filtered, we know that its parents are not either. So we can take a shortcut. This shortcut avoid the computation of all filtered revs in some cases. Differential Revision: https://phab.mercurial-scm.org/D7487

locarepo: also fastpath `nullid` lookup in __getitem__ We already use that fastpath for `"null"` and `nullrev`, using it for `nullid` is similar. Differential Revision: https://phab.mercurial-scm.org/D7486