phases: sparsify phaseroots and phasesets
As final step of dealing with the holes in the phase numbers, make
phaseroots and phasesets both dictionaries indexed by the phase number.
Further adjust the interface of the C module by pushing the node to
revision mapping down as it is cheaper on the C side to deal with
revision numbers.
Overall, the patch series improves a no-change "hg up" for my NetBSD test
repository from 4.7s to 1.3s.
Differential Revision: https://phab.mercurial-scm.org/D8698
$ hg init
$ "$PYTHON" -c 'open("a", "wb").write(b"confuse str.splitlines\nembedded\rnewline\n")'
$ hg ci -Ama -d '1 0'
adding a
$ echo clean diff >> a
$ hg ci -mb -d '2 0'
$ hg diff -r0 -r1
diff -r 107ba6f817b5 -r 310ce7989cdc a
--- a/a Thu Jan 01 00:00:01 1970 +0000
+++ b/a Thu Jan 01 00:00:02 1970 +0000
@@ -1,2 +1,3 @@
confuse str.splitlines
embedded\r (no-eol) (esc)
newline
+clean diff