tests/test-debug-rebuild-dirstate.t

phases: invalidate the phases set less often on retract boundary

We already have the information to update the phase set, so we do so directly
instead of invalidating the cache.

This show a sizeable speedup in our `perf::unbundle` benchmark on the
many-draft mozilla-try repository.

### data-env-vars.name            = mozilla-try-2023-03-22-zstd-sparse-revlog
  # benchmark.name                = hg.perf.perf-unbundle
  # bin-env-vars.hg.flavor        = no-rust
  # bin-env-vars.hg.py-re2-module = default
  # benchmark.variants.issue6528  = disabled

  # benchmark.variants.revs = last-10
before: 2.055259 seconds
after:  1.887064 seconds (-8.18%)
  # benchmark.variants.revs = last-100
before: 2.409239 seconds
after:  2.222429 seconds (-7.75%)
  # benchmark.variants.revs = last-1000
before: 3.945648 seconds
after:  3.762480 seconds (-4.64%)

#require rust

  $ cat >> $HGRCPATH << EOF
  > [format]
  > use-dirstate-v2=1
  > [storage]
  > dirstate-v2.slow-path=allow
  > EOF

  $ hg init t
  $ cd t

  $ for i in 1 2 3 4 5 6 7 8 9 10; do touch foobar$i; done
  $ hg add .
  adding foobar1
  adding foobar10
  adding foobar2
  adding foobar3
  adding foobar4
  adding foobar5
  adding foobar6
  adding foobar7
  adding foobar8
  adding foobar9
  $ hg commit -m "1"

Check that there's no space leak on debugrebuilddirstate

  $ f --size .hg/dirstate*
  .hg/dirstate: size=133
  .hg/dirstate.88698448: size=511
  $ hg debugrebuilddirstate
  $ f --size .hg/dirstate*
  .hg/dirstate: size=133
  .hg/dirstate.6b8ab34b: size=511
  $ hg debugrebuilddirstate
  $ f --size .hg/dirstate*
  .hg/dirstate: size=133
  .hg/dirstate.b875dfc5: size=511