fix: Resolve flaky NotInParallel test by using ConcurrentDictionary (#1679)

The test NotInParallel_If_Any_Modules_Executing_With_Any_Of_Same_ConstraintKey
was flaky due to two issues:

1. Using ConcurrentBag with TryTake() which removes an arbitrary item,
   not the specific module name that was added. This corrupted tracking
   when multiple modules were executing concurrently.

2. Missing [TUnit.Core.NotInParallel] attribute on the test class, which
   could cause interference when tests run in parallel and share static state.

The fix replaces ConcurrentBag with ConcurrentDictionary to ensure each
module correctly removes only its own entry from the tracking collection,
matching the pattern used in NotInParallelTestsWithConstraintKeys.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: thomhurst

test/ModularPipelines.UnitTests/NotInParallelTestsWithMultipleConstraintKeys.cs

@@ -5,9 +5,12 @@
 
 namespace ModularPipelines.UnitTests;
 
+[TUnit.Core.NotInParallel]
 public class NotInParallelTestsWithMultipleConstraintKeys : TestBase
 {
-    private static readonly ConcurrentBag<string> _executingModules = new();
+    // Use ConcurrentDictionary instead of ConcurrentBag to ensure we remove the correct entry
+    // ConcurrentBag.TryTake() removes an arbitrary item, which corrupts tracking
+    private static readonly ConcurrentDictionary<string, bool> _executingModules = new();
     private static readonly ConcurrentBag<string> _violations = new();
 
     [ModularPipelines.Attributes.NotInParallel("A")]
@@ -17,17 +20,17 @@ public class Module1 : Module<string>
         {
             var moduleName = GetType().Name;
 
-            _executingModules.Add(moduleName);
+            _executingModules[moduleName] = true;
             await Task.Delay(50, cancellationToken);
 
-            if (_executingModules.Contains("Module2"))
+            if (_executingModules.ContainsKey("Module2"))
             {
                 _violations.Add($"{moduleName} started while Module2 was executing (both have 'A')");
             }
 
             await Task.Delay(50, cancellationToken);
 
-            _executingModules.TryTake(out _);
+            _executingModules.TryRemove(moduleName, out _);
             return moduleName;
         }
     }
@@ -39,22 +42,22 @@ public class Module2 : Module<string>
         {
             var moduleName = GetType().Name;
 
-            _executingModules.Add(moduleName);
+            _executingModules[moduleName] = true;
             await Task.Delay(50, cancellationToken);
 
-            if (_executingModules.Contains("Module1"))
+            if (_executingModules.ContainsKey("Module1"))
             {
                 _violations.Add($"{moduleName} started while Module1 was executing (both have 'A')");
             }
 
-            if (_executingModules.Contains("Module3"))
+            if (_executingModules.ContainsKey("Module3"))
             {
                 _violations.Add($"{moduleName} started while Module3 was executing (both have 'B')");
             }
 
             await Task.Delay(50, cancellationToken);
 
-            _executingModules.TryTake(out _);
+            _executingModules.TryRemove(moduleName, out _);
             return moduleName;
         }
     }
@@ -66,17 +69,17 @@ public class Module3 : Module<string>
         {
             var moduleName = GetType().Name;
 
-            _executingModules.Add(moduleName);
+            _executingModules[moduleName] = true;
             await Task.Delay(50, cancellationToken);
 
-            if (_executingModules.Contains("Module2"))
+            if (_executingModules.ContainsKey("Module2"))
             {
                 _violations.Add($"{moduleName} started while Module2 was executing (both have 'B')");
             }
 
             await Task.Delay(50, cancellationToken);
 
-            _executingModules.TryTake(out _);
+            _executingModules.TryRemove(moduleName, out _);
             return moduleName;
         }
     }
@@ -87,11 +90,11 @@ public class Module4 : Module<string>
         public override async Task<string?> ExecuteAsync(IModuleContext context, CancellationToken cancellationToken)
         {
             var moduleName = GetType().Name;
-            _executingModules.Add(moduleName);
+            _executingModules[moduleName] = true;
 
             await Task.Delay(100, cancellationToken);
 
-            _executingModules.TryTake(out _);
+            _executingModules.TryRemove(moduleName, out _);
             return moduleName;
         }
     }