Double-check the "remove" behavior from the MMKVParser

[spak9]

The decode_into_map() function currently does not indicate whether a key-value pair has been removed, which may be useful for the inclined analyst.

For example, the following Android code simply encodes ('key', 4444) pair, and then removes it right after:

  private void createInt32KeypairWithRemove() {
      deleteMMKVFiles("data_int32_keypair_with_remove");

      MMKV kv = MMKV.mmkvWithID("data_int32_keypair_with_remove");
      kv.encode("key", 4444);
      kv.removeValueForKey("key");

      int value = kv.decodeInt("key"); // default = 0
      Log.d("MMKV", "key after remove = " + value);
  }

The corresponding decode_into_map() call returns [b'\xdc"'], which is correct, but can be argued that it should have an additional element that indicates a removal, such as a None or something of that nature.