subranges: migrate handling of single element range This is the simplest case by far, so we start with that one. We still use the rich object as an argument, but we'll do our best to not relying on that. This is important for performance reason.

stablerange: move the subrange cache into our new class This is the first step toward having more logic in that class

depth: extract code dedicated to depth of a merge in its own function The merge case is more complicated than the regular one, we extract is for the sake of clarity.

stablerange: move 'depth' inside a new 'stablerange' module The stablerange used for discovery requires significant amount of code. There is algorithme, cache, cache persistence, etc. So we create a dedicated module for it. The function is directly moved into a rich class handling cache (for now in memory) because we know we will need it.

obsdiscovery: document the status of the module I figured i would be useful to document what we expect from the code in each module.

split: move the debugcommand into a dedicated module The code related to debugobsstorestat is fairly independant, we move it into its own module.

legacy: move 'debugrecordpruneparents' in the extensions The transition is a couple of year old now, repository with the old format must be quite hard to find by now.

checks: correct the shebang line filtering for python files As it is, the only related file is docs/test2rst.py, which was covered by **.py. Not sure if it matters, but most patterns in core tests are for "#!.*?python". (Though there are a couple "#!.*python" tests.)