Use unordered maps for VST3 plugin instances

The better algorithmic time complexity should help when using many (say,
hundreds) of instances of a single VST3 plugin.

CHANGELOG.md

@@ -14,6 +14,8 @@ Versioning](https://semver.org/spec/v2.0.0.html).
   completely rewritten to use both shared memory and message passing to reduce
   expensive memory copies to a minimum. With this change the DSP load overhead
   during audio processing should now be about as low as it's going to get.
+- Optimized the management of VST3 plugin instances to reduce the overhead when
+  using many instances of a VST3 plugin.
 - Prevented some more potential unnecessary memory operations during yabridge's
   communication. The underlying serialization library was recreating some
   objects even when that wasn't needed, which could in theory result in memory

src/common/communication/common.h

@@ -744,7 +744,7 @@ class AdHocSocketHandler {
 
         // This works the exact same was as `active_plugins` and
         // `next_plugin_id` in `GroupBridge`
-        std::map<size_t, Thread> active_secondary_requests{};
+        std::unordered_map<size_t, Thread> active_secondary_requests{};
         std::atomic_size_t next_request_id{};
         std::mutex active_secondary_requests_mutex{};
         accept_requests(

src/common/communication/vst3.h

@@ -526,7 +526,8 @@ class Vst3Sockets final : public Sockets {
      * would have one dedicated thread for handling function calls to these
      * interfaces, and then another dedicated thread just idling around.
      */
-    std::map<size_t, Vst3MessageHandler<Thread, AudioProcessorRequest>>
+    std::unordered_map<size_t,
+                       Vst3MessageHandler<Thread, AudioProcessorRequest>>
         audio_processor_sockets;
     std::mutex audio_processor_sockets_mutex;
 };

src/plugin/bridges/vst3-impls/plugin-proxy.h

@@ -529,7 +529,7 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
         /**
          * Memoizes `IEditController::getParameterInfo()`.
          */
-        std::map<int32, Steinberg::Vst::ParameterInfo> parameter_info;
+        std::unordered_map<int32, Steinberg::Vst::ParameterInfo> parameter_info;
     };
 
     /**

src/plugin/bridges/vst3.h

@@ -204,7 +204,7 @@ class Vst3PluginBridge : PluginBridge<Vst3Sockets<std::jthread>> {
      * `register_plugin_proxy()` in the constractor, and an instance is then
      * removed through a call to `unregister_plugin_proxy()` in the destructor.
      */
-    std::map<size_t, std::reference_wrapper<Vst3PluginProxyImpl>>
+    std::unordered_map<size_t, std::reference_wrapper<Vst3PluginProxyImpl>>
         plugin_proxies;
 
    private:

src/wine-host/bridges/vst3.h

@@ -440,7 +440,7 @@ class Vst3Bridge : public HostBridge {
      * will cause all pointers to it to get dropped and the object to be cleaned
      * up.
      */
-    std::map<size_t, InstanceInterfaces> object_instances;
+    std::unordered_map<size_t, InstanceInterfaces> object_instances;
     std::mutex object_instances_mutex;
 
     /**