feat: Catch and print IO errors

Main.lean

@@ -33,11 +33,16 @@ partial def loop : MainM Unit := do
     -- Using `Lean.Json.compress` here to prevent newline
     IO.println error.compress
   | .ok command =>
+    try
       let ret ← execute command
       let str := match state.options.printJsonPretty with
         | true => ret.pretty
         | false => ret.compress
       IO.println str
+    catch e =>
+      let message ← e.toMessageData.toString
+      let error  := Lean.toJson ({ error := "io", desc := message }: InteractionError)
+      IO.println error.compress
   loop