* feat: Add bench layout classes and configuration handler
Bench layout: (`frappe.bench`)
- Layout by env variable, e.g. FRAPPE_BENCH_PATH, FRAPPE_SITES_PATH, etc
- Detecting modules and apps by the presence of a sentinel .frappe file
- Site is scoped by frappe.local.site_name (thread safe)
Config handler: (`frappe.bench.sites{,.site}.config`)
- Optional config registry for better discovery; warning if not specced
- Env variable overload with `FRAPPE_` prefix
* chore: type frappe.config
* chore: type frappe.bencher
* chore: py310 compat
