Merge pull request #382 from loresoft/claude/mapping-diagnostic-analyzer-F7SLG

Add DiagnosticAnalyzer for Arbiter.Mapping.Generators to validate mapper classes

Author: pwelter34

src/Arbiter.Mapping.Generators/Infrastructure/IndentedStringBuilder.cs

@@ -248,7 +248,7 @@ private void DoIndent()
         _indentPending = false;
     }
 
-    private sealed class Indenter : IDisposable
+    private readonly struct Indenter : IDisposable
     {
         private readonly IndentedStringBuilder _stringBuilder;
 
@@ -263,7 +263,7 @@ public void Dispose()
             => _stringBuilder.DecrementIndent();
     }
 
-    private sealed class IndentSuspender : IDisposable
+    private readonly struct IndentSuspender : IDisposable
     {
         private readonly IndentedStringBuilder _stringBuilder;
         private readonly byte _indent;