phases: introduce a performant efficient way to access revision in a set This will be useful in the next changesets.

phases: use revision number in `_pushdiscoveryphase` We now reach our target checkpoint in terms of rev-num conversion. The `_pushdiscoveryphase` function is now performing graph computation based on revision number only. Avoiding repeated conversion from node-id to rev-num. See previous changeset updated `new_heads` for rationnal. Again, time saved in the 100 milliseconds order of magnitude for the mozilla-try benchmark I have been using. However, wow that the logic is done using revision number, we can look into having better logic in the next changesets, which will provide a much bigger speedup.

phases: move RemotePhasesSummary to revision number This continue our quest to align more logic on revision number instead of node-ids. The motivation is similar to the change to `new_heads` and `analyze_remote_phases` a few changeset earlier. Again, we take this as an opportunity to rename the class, and the attribute to the new naming scheme. This will highlight the need for code update for any code using it an expecting node-ids. Many of the rev-num → node-id conversion we had to introduce in the previous changesets can now be removed. More will be removed in the future as we continue to align code toward rev-num usage. time saved in the 100 milliseconds order of magnitude for the mozilla-try benchmark I have been using.

phases: stop using `repo.set` in `remotephasessummary` The `repository.set` create changectx on the fly, an expensive operation. Using `repo.revs` and a direct rev-num → node-id translation will be significantly faster. This is especially true as we prepare ourself to no longer do the rev-num → node-id transalation there. The speedup is a bit lost in the overall noisyness of the slow phase discovery algorithm, but it save a small amount of time in my benchmark.

phases: use revision number in analyze_remote_phases Same logic as the previous change to `new_heads`, see rationnal there. This avoids a small number of `nodes -> revs` conversion speeding thing up in the 100 milliseconds order of magnitude for the worses cases. However, the rest of the logic is noisy enough that it hardly matters for now.

phases: use revision number in new_heads All graph operations will be done using revision numbers, so passing nodes only means they will eventually get converted to revision numbers internally. As part of an effort to align the code on using revision number we make the `phases.newheads` function operated on revision number, taking them as input and using them in returns, instead of the node-id it used to consume and produce. This is part of multiple changesets effort to translate more part of the logic, but is done step by step to facilitate the identification of issue that might arise in mercurial core and extensions. To make the change simpler to handle for third party extensions, we also rename the function, using a more modern form. This will help detecting the different between the node-id version and the rev-num version. I also take this as an opportunity to add some comment about possible performance improvement for the future. They don't matter too much now, but they are worse exploring in a while.

phases: convert remote phase root to node while reading them This is currently a bit silly as we will convert them back to node right after, but that is an intermediate step before doing more disruptive changes.

phases: more compact error handling in analyzeremotephases using an intermediate variable result in more readable code, so let us use it.