message: Add position getters to the binary deserializer
diff: @@ -57,6 +57,18 @@ public:
  error apply_raw(size_t num_bytes, void* data) override;
  + // -- properties -------------------------------------------------------------
  +
  + /// Returns the current read position.
  + const char* pos() const {
  + return pos_;
  + }
  +
  + /// Returns the past-the-end iterator.
  + const char* end() const {
  + return end_;
  + }
  +
  protected:
  error apply_impl(int8_t&) override;
  