Psutil-extra

Changelog:

- Implement `proc_getgroups()` on OpenBSD
- Add `proc_getpgid()` and `proc_getsid()` helpers (can get process group ID/session ID even if `os.getpgid()`/`os.getsid()` raise permission errors)
- Handle `psutil.PROCFS_PATH` not being set (gracefully falls back on `/proc`)
- Add `oneshot_proc()` caching context manager to improve performance in some cases
- Add `proc_as_dict()` helper
- Add `proc_get_sigmasks()` function (on some platforms)
- FreeBSD: Handle operations on PID 0 properly

Initial release.

Current OS support for various functions

- Linux (tested in CI): `proc_get_umask()`, `proc_getgroups()`, `proc_rlimit()`, `proc_getrlimit()`
- FreeBSD (tested in CI): `proc_get_umask()`, `proc_getgroups()`, `proc_rlimit()`, `proc_getrlimit()`
- macOS (tested in CI): `proc_getgroups()`
- NetBSD (not tested in CI): `proc_getgroups()`, `proc_rlimit()`, `proc_getrlimit()`
- DragonflyBSD (not tested in CI): `proc_getgroups()`, `proc_getrlimit()`
- Solaris (not tested in CI): `proc_getgroups()`