phase-shelve: honor and prefer obs shelves for existence and modified time

phase-shelve: read patch details from a (possibly internal) node in the repo

phase-shelve: Extract function for _optimized_match for re-use

obsstore: break the repo → obstore → repo loop This should help the garbage collector to do its job. On repository with many markers, the memory pressure from the obsstore can get quite serious.

relnotes: mention chg behavior change when given --cwd

dispatch: change cwd when loading local config Previously, the `_getlocal` function would not correctly load the repo config when given a relative `rpath` and an alternate cwd via the `wd` parameter. Normally when `--cwd` is specified, hg changes to the given directory before attempting to load the local config (and therefore does not specify a `wd`). The only time the function is called with `wd` set is when hg is running as a command server (e.g., with chg), in which case each forked worker process will attempt to configure itself via `_getlocal` before responding to the client. When given a relative repo path, the worker fails to load the repo config, detects a config mismatch with the client, and enters a redirect/respawn loop. To fix this, we can simply change to the desired working directory during config loading. (Note that simply concatenating `wd` and `rpath` won't work in all cases. The repo path could be something more complicated than a simple relative path, such as a `union:` repo.)

rust-status: ignored directories are now correctly only listed if opted into This fixes the behavior of `hg purge` removing empty ignored directory even without `--all` or `--ignored`.

test: show how purge removes ignored directories Apparently the rust code path removes ignored directories even though the pure code path doesn't. Show this in tests.

contrib: add support for rhel9

packagelib: use python3 by default