internal/rosa: evaluate packages from fs

This migrates GNU sed to azalea, and resulting IR matches.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/mbf/main.go

@@ -64,11 +64,11 @@ func main() {
 			return
 		}
 
-		h, ok := r.(rosa.HandleError)
+		e, ok := r.(rosa.LoadError)
 		if !ok {
 			panic(r)
 		}
-		log.Fatal(h)
+		log.Fatal(e)
 	}()
 
 	ctx, stop := signal.NotifyContext(context.Background(),