style: apply CSharpier formatting to all C# sources

Repo-wide sweep with the pinned CSharpier 1.3.0 tool. Whitespace and
line-wrapping only; OpenNest.Engine.Tests (109) and OpenNest.IO.Tests
pass after reformat, full solution builds 0 errors.

Added .csharpierignore so csproj/config XML keeps its existing layout
(CSharpier's XML wrapping churns attributes with zero benefit).

Formatting is now enforceable: dotnet csharpier check . passes.

OpenNest.Mcp/Program.cs

@@ -5,8 +5,8 @@ using OpenNest.Mcp;
 var builder = Host.CreateApplicationBuilder(args);
 
 builder.Services.AddSingleton<NestSession>();
-builder.Services
-    .AddMcpServer()
+builder
+    .Services.AddMcpServer()
     .WithStdioServerTransport()
     .WithToolsFromAssembly(typeof(Program).Assembly);