tests/test-mq-qsave.t

rust-dirstatemap: add `NonNormalEntries` class

This fix introduces the same encapsulation as the `copymap`. There is no easy
way of doing this any better for now.

`hg up -r null && time HGRCPATH= HGMODULEPOLICY=rust+c hg up tip` on Mozilla
Central, (not super recent, but it doesn't matter):

Before: 7:44,08 total
After: 1:03,23 total

Pretty brutal regression!

This is a graft on stable of cf1f8660e568

Differential Revision: https://phab.mercurial-scm.org/D8111

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "mq=" >> $HGRCPATH

  $ hg init

  $ echo 'base' > base
  $ hg ci -Ambase
  adding base

  $ hg qnew -mmqbase mqbase

  $ hg qsave
  $ hg qrestore 2
  restoring status: hg patches saved state