perf: extract the timing of a section in a context manager This makes it easier to reuse it in other (future) part of the code that requires their own time management.

pref: support negative indexing in perfrevlogrevisions This is useful to check for a consistent final slice in multiple different repositories.

perf: accept formatter option for perfmanifest

perf: fix -T json The previous code was mixing formatting and data, breaking `-T json` with unexpected data. We fix the issue and add a test to prevent future regression.

formatter: more details on assertion failure This is useful when the assertion fails.

wireprotov2: raise ProgrammingError on unknown action Suggested by @durin42 in review of D4923. Differential Revision: https://phab.mercurial-scm.org/D4935