Support standard GRANIAN_* env vars and the rloop event loop

- Launcher now only injects --interface/--host/--port when the matching
  GRANIAN_* env var is unset, so every granian option (GRANIAN_LOOP,
  GRANIAN_WORKERS, GRANIAN_HTTP, GRANIAN_HOST, GRANIAN_PORT, ...) can be
  configured via granian's standard GRANIAN_* environment variables
- Add the rloop event loop as a runtime dependency so GRANIAN_LOOP=rloop
  works out of the box (previously failed with a missing 'rloop' package)

pyproject.toml

@@ -26,6 +26,7 @@ dependencies = [
 server = [
     "kaya-rsgi",
     "granian",
+    "rloop",
 ]
 dev = [
     "httpx",