fix: incorrect router hb_maps:get/3 Opts-as-fallback

[charmful0x]

following the hb_maps:get/3 default misuse checks (#701), i patched another one in dev_router (Nearest strategy path)

issue

in choose/5 for <<"Nearest">>, this was using hb_maps:get(<<"wallet">>, Node, Opts) - which means Opts was being passed as default -> confusing errors if missing

patched to explicit handling with arity 4 + fail fast:

  Wallet =
      case hb_maps:get(<<"wallet">>, Node, not_found, Opts) of
          W when is_binary(W) -> W;
          not_found -> throw({error, wallet_not_found});
          _ -> throw({error, invalid_wallet})
      end,

also patched the same in preprocess/3, at user path extraction

            UserPath =
                case hb_maps:get(<<"path">>, Req, not_found, Opts) of
                    P when is_binary(P), byte_size(P) > 0 ->
                        P;
                    not_found ->
                        throw({error, missing_user_path});
                    _ ->
                        throw({error, invalid_user_path})
                end,

^ it was hb_maps:get(<<"path">>, Req, Opts)

all tests pass

  [done in 17.863 s]
=======================================================
  All 30 tests passed.