Allow deserialization into an existing object

We're going to need this for VST3 because we're going to have to
explicitly instantiate our interface implementations since they need to
be able to perform complicated callbacks.

src/common/communication/common.h

@@ -92,6 +92,8 @@ inline void write_object(Socket& socket, const T& object) {
  * @param socket The Boost.Asio socket to read from.
  * @param buffer The buffer to read into. This is useful for sending audio and
  *   chunk data since that can vary in size by a lot.
+ * @param object The object to serialize into. There are also overrides that
+ *   create a new default initialized `T`
  *
  * @return The deserialized object.
  *
@@ -102,7 +104,7 @@ inline void write_object(Socket& socket, const T& object) {
  * @relates write_object
  */
 template <typename T, typename Socket>
-inline T read_object(Socket& socket, std::vector<uint8_t>& buffer) {
+inline T read_object(Socket& socket, std::vector<uint8_t>& buffer, T& object) {
     // See the note above on the use of `uint64_t` instead of `size_t`
     std::array<uint64_t, 1> message_length;
     boost::asio::read(socket, boost::asio::buffer(message_length));
@@ -118,7 +120,6 @@ inline T read_object(Socket& socket, std::vector<uint8_t>& buffer) {
         boost::asio::read(socket, boost::asio::buffer(buffer));
     assert(size == actual_size);
 
-    T object;
     auto [_, success] =
         bitsery::quickDeserialization<InputAdapter<std::vector<uint8_t>>>(
             {buffer.begin(), size}, object);
@@ -132,14 +133,40 @@ inline T read_object(Socket& socket, std::vector<uint8_t>& buffer) {
 }
 
 /**
- * `read_object()` with a small default buffer for convenience.
+ * `read_object()` into a new default initialized object with an existing
+ * buffer.
+ *
+ * @overload
+ */
+template <typename T, typename Socket>
+inline T read_object(Socket& socket, std::vector<uint8_t>& buffer) {
+    T object;
+    return read_object<T>(socket, buffer, object);
+}
+
+/**
+ * `read_object()` into an existing object a small default
+ * buffer for convenience.
+ *
+ * @overload
+ */
+template <typename T, typename Socket>
+inline T read_object(Socket& socket, T& object) {
+    std::vector<uint8_t> buffer(64);
+    return read_object<T>(socket, buffer, object);
+}
+
+/**
+ * `read_object()` into a new default initialized object with a small default
+ * buffer for convenience.
  *
  * @overload
  */
 template <typename T, typename Socket>
 inline T read_object(Socket& socket) {
+    T object;
     std::vector<uint8_t> buffer(64);
-    return read_object<T>(socket, buffer);
+    return read_object<T>(socket, buffer, object);
 }
 
 /**