Use unique_ptr instead of shared_ptr for PluginInterface pointers

unique_ptr is simpler, and can be easily converted to shared_ptr if needed, and makes it obvious that each call will return a new pointer.

This does mean that if I want to hold onto the objects again in the future for some reason, that'll need the API to change back, but that seems unlikely.

unique_ptr not being copyable does make using it a little more awkward, but that only happened in one place in LOOT's code, and there the pointer needs to become shared anyway.

cpp/include/loot/game_interface.h

@@ -141,22 +141,18 @@ public:
    * @brief Get data for a loaded plugin.
    * @param  pluginName
    *         The filename of the plugin to get data for.
-   * @returns A shared pointer to a const PluginInterface implementation. The
-   *          pointer is null if the given plugin has not been loaded. Repeated
-   *          calls given the same filename may return different pointers to
-   *          equivalent objects.
+   * @returns A pointer to a const PluginInterface implementation. The
+   *          pointer is null if the given plugin has not been loaded.
    */
-  virtual std::shared_ptr<const PluginInterface> GetPlugin(
+  virtual std::unique_ptr<const PluginInterface> GetPlugin(
       std::string_view pluginName) const = 0;
 
   /**
    * @brief Get a set of const references to all loaded plugins' PluginInterface
    *        objects.
-   * @returns A set of shared pointers to const PluginInterface objects.
-   *          Repeated calls may return different pointers to equivalent
-   *          objects.
+   * @returns A set of pointers to const PluginInterface objects.
    */
-  virtual std::vector<std::shared_ptr<const PluginInterface>> GetLoadedPlugins()
+  virtual std::vector<std::unique_ptr<const PluginInterface>> GetLoadedPlugins()
       const = 0;
 
   /**

cpp/src/api/game.cpp

@@ -171,7 +171,7 @@ void Game::LoadPlugins(const std::vector<std::filesystem::path>& pluginPaths,
 
 void Game::ClearLoadedPlugins() { game_->clear_loaded_plugins(); }
 
-std::shared_ptr<const PluginInterface> Game::GetPlugin(
+std::unique_ptr<const PluginInterface> Game::GetPlugin(
     std::string_view pluginName) const {
   const auto pluginOpt = game_->plugin(convert(pluginName));
   if (!pluginOpt->is_some()) {
@@ -179,19 +179,19 @@ std::shared_ptr<const PluginInterface> Game::GetPlugin(
   }
 
   try {
-    return std::make_shared<Plugin>(
+    return std::make_unique<Plugin>(
         std::move(pluginOpt->as_ref().boxed_clone()));
   } catch (const ::rust::Error& e) {
     std::rethrow_exception(mapError(e));
   }
 }
 
-std::vector<std::shared_ptr<const PluginInterface>> Game::GetLoadedPlugins()
+std::vector<std::unique_ptr<const PluginInterface>> Game::GetLoadedPlugins()
     const {
-  std::vector<std::shared_ptr<const PluginInterface>> plugins;
+  std::vector<std::unique_ptr<const PluginInterface>> plugins;
   for (const auto& pluginRef : game_->loaded_plugins()) {
     plugins.push_back(
-        std::make_shared<Plugin>(std::move(pluginRef.boxed_clone())));
+        std::make_unique<Plugin>(std::move(pluginRef.boxed_clone())));
   }
 
   return plugins;

cpp/src/api/game.h

@@ -35,10 +35,10 @@ public:
 
   void ClearLoadedPlugins() override;
 
-  std::shared_ptr<const PluginInterface> GetPlugin(
+  std::unique_ptr<const PluginInterface> GetPlugin(
       std::string_view pluginName) const override;
 
-  std::vector<std::shared_ptr<const PluginInterface>> GetLoadedPlugins()
+  std::vector<std::unique_ptr<const PluginInterface>> GetLoadedPlugins()
       const override;
 
   std::vector<std::string> SortPlugins(