Use verbatim string literals for F# directives

Use C# verbatim string literals (@"...") when composing F# script directives to avoid escaping issues with Windows paths. Updated #r, #load and #I generation to produce @"path" in FSharpKernel.cs, NuGetReferenceProcessor.cs and ScriptDirectiveProcessor.cs so embedded file paths are handled correctly.

Author: TorreyBetts

src/Verso.FSharp/Kernel/FSharpKernel.cs

@@ -150,7 +150,7 @@ public Task InitializeAsync()
         var abstractionsAssembly = typeof(Verso.Abstractions.IVariableStore).Assembly.Location;
         if (!string.IsNullOrEmpty(abstractionsAssembly))
         {
-            _sessionManager.EvalSilent($"#r \"{abstractionsAssembly}\"");
+            _sessionManager.EvalSilent($"#r @\"{abstractionsAssembly}\"");
         }
 
         _variableBridge = new VariableBridge(_options);
@@ -216,7 +216,7 @@ public async Task<IReadOnlyList<CellOutput>> ExecuteAsync(string code, IExecutio
             var magicPaths = _nugetProcessor!.CheckMagicCommandResults(context.Variables);
             foreach (var path in magicPaths)
             {
-                _sessionManager!.EvalSilent($"#r \"{path}\"");
+                _sessionManager!.EvalSilent($"#r @\"{path}\"");
                 _projectContext?.AddReference(path);
                 var dir = Path.GetDirectoryName(path);
                 if (dir is not null)

src/Verso.FSharp/NuGet/NuGetReferenceProcessor.cs

@@ -133,7 +133,7 @@ public async Task<NuGetProcessResult> ProcessAsync(
                 if (_resolvedAssemblyPaths.Add(assemblyPath))
                 {
                     newPaths.Add(assemblyPath);
-                    session.EvalSilent($"#r \"{assemblyPath}\"");
+                    session.EvalSilent($"#r @\"{assemblyPath}\"");
                     var dir = Path.GetDirectoryName(assemblyPath);
                     if (dir is not null)
                         session.AddNuGetAssemblyDirectory(dir);

src/Verso.FSharp/NuGet/ScriptDirectiveProcessor.cs

@@ -61,7 +61,7 @@ public string ProcessDirectives(string code, INotebookMetadata? metadata)
             var resolved = ResolvePath(relativePath, metadata);
             if (File.Exists(resolved) && !_resolvedAssemblyPaths.Contains(resolved))
                 _resolvedAssemblyPaths.Add(resolved);
-            return $"#r \"{resolved}\"";
+            return $"#r @\"{resolved}\"";
         });
 
         // Process #load "script.fsx"
@@ -71,15 +71,15 @@ public string ProcessDirectives(string code, INotebookMetadata? metadata)
             var resolved = ResolvePath(relativePath, metadata);
             if (File.Exists(resolved) && !_loadedFilePaths.Contains(resolved))
                 _loadedFilePaths.Add(resolved);
-            return $"#load \"{resolved}\"";
+            return $"#load @\"{resolved}\"";
         });
 
         // Process #I "path"
         processed = IncludePathRegex.Replace(processed, match =>
         {
             var relativePath = match.Groups[1].Value;
             var resolved = ResolvePath(relativePath, metadata);
-            return $"#I \"{resolved}\"";
+            return $"#I @\"{resolved}\"";
         });
 
         // Process #nowarn "number"