feat(core): add PluginLoader with collectible ALC

src/AcDream.Core/Plugins/PluginLoader.cs

@@ -0,0 +1,34 @@
+using System.Reflection;
+using AcDream.Plugin.Abstractions;
+
+namespace AcDream.Core.Plugins;
+
+public static class PluginLoader
+{
+    public static LoadedPlugin Load(string pluginDirectory, PluginManifest manifest, IPluginHost host)
+    {
+        var dllPath = Path.Combine(pluginDirectory, manifest.EntryDll);
+        if (!File.Exists(dllPath))
+            return new LoadedPlugin(manifest, null, $"entry dll not found: {dllPath}");
+
+        try
+        {
+            var alc = new PluginAssemblyLoadContext(pluginDirectory, dllPath);
+            var asm = alc.LoadFromAssemblyPath(dllPath);
+
+            var pluginType = asm.GetTypes()
+                .FirstOrDefault(t => !t.IsAbstract && typeof(IAcDreamPlugin).IsAssignableFrom(t));
+
+            if (pluginType is null)
+                return new LoadedPlugin(manifest, null, $"no IAcDreamPlugin implementation found in {manifest.EntryDll}");
+
+            var instance = (IAcDreamPlugin)Activator.CreateInstance(pluginType)!;
+            instance.Initialize(host);
+            return new LoadedPlugin(manifest, instance, null);
+        }
+        catch (Exception ex)
+        {
+            return new LoadedPlugin(manifest, null, $"{ex.GetType().Name}: {ex.Message}");
+        }
+    }
+}