rust-revlog: bare minimal NodeTree exposition The independent `NodeTree` instances needs to be associated to an index (for forward-checks of candidates) but do not need to encompass all revisions from that index. This is exactly how it is used in `scmutil.shortesthenodeidprefix` and we restrict the implementation to the bare minimum needed there and to write convincing tests. It would of course be fairly trivial to add more.

BasedOnStyle: LLVM
IndentWidth: 8
UseTab: ForIndentation
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
IncludeCategories:
  - Regex:           '^<'
    Priority:        1
  - Regex:           '^"'
    Priority:        2