[be] add example endpoint

AtmoType/AtmoType.csproj

···
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="FastEndpoints" Version="7.1.1" />
     <PackageReference Include="FishyFlip" Version="4.2.0" />
   </ItemGroup>
 

AtmoType/Endpoints/Example/Example.cs

···
+namespace AtmoType.Endpoints.Example;
+
+public class ExampleRequest
+{
+    public string? Name { get; set; }
+}
+
+public class ExampleResponse
+{
+    public string Hello { get; set; } = string.Empty;
+}
+
+public class Example : XrpcQuery<ExampleRequest, ExampleResponse>
+{
+    public override string Nsid => "win.atmotype.example.example";
+
+    public override async Task<ExampleResponse> ExecuteAsync(ExampleRequest req, CancellationToken ct)
+    {
+        return new ExampleResponse
+        {
+            Hello = "world"
+        };
+    }
+}

AtmoType/Program.cs

···
+using FastEndpoints;
+
 var builder = WebApplication.CreateBuilder(args);
+builder.Services.AddFastEndpoints();
 var app = builder.Build();
 
+app.UseFastEndpoints();
 app.MapGet("/", () => "Hello World!");
-
 app.Run();

AtmoType/XrpcBase.cs

···
+using FastEndpoints;
+
+namespace AtmoType;
+
+public abstract class XrpcQuery<TRequest, TResponse> : Endpoint<TRequest, TResponse>
+    where TRequest : notnull
+    where TResponse : notnull
+{
+    public abstract string Nsid { get; }
+
+    public override void Configure()
+    {
+        Get($"/xrpc/{Nsid}");
+        AllowAnonymous(); // TODO: Better auth support
+    }
+}
+
+public abstract class XrpcProcedure<TRequest, TResponse> : Endpoint<TRequest, TResponse>
+    where TRequest : notnull
+    where TResponse : notnull
+{
+    public abstract string Nsid { get; }
+
+    public override void Configure()
+    {
+        Post($"/xrpc/{Nsid}");
+        AllowAnonymous(); // TODO: Better auth support
+    }
+}