b32: add test + rm padding

test/b32.ml

@@ -0,0 +1,15 @@
+let () =
+  let id s = s |> B32.encode |> B32.decode |> Result.get_ok in
+  let f s =
+    let s' = id s in
+    match s' = s with
+    | false ->
+        Fmt.failwith "b32 round trip failure: @\nin :`%S`@\nout:`%S`" s' s
+    | true -> ()
+  in
+  let s = String.init 0xff Char.chr in
+  let s_l = List.init 0x0f (fun i -> String.init i Char.chr) in
+  f s;
+  List.iter f s_l;
+
+  ()