docs: Add explanatory remarks for ModuleResult<T?> signature

The signature uses ModuleResult<T?> because Module<T>.GetAwaiter() returns
ModuleResult<T?>, matching the nullable return type of ExecuteAsync.
This is intentional and matches the framework's design.

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

Author: thomhurst

test/ModularPipelines.TestHelpers/Assertions/ModuleResultAssertions.cs

@@ -12,6 +12,10 @@ public static class ModuleResultAssertions
     /// Asserts that a module result represents a successful execution with a non-null value.
     /// Checks: ModuleResultType is Success, Exception is null, Value is not null.
     /// </summary>
+    /// <remarks>
+    /// The signature uses <c>ModuleResult&lt;T?&gt;</c> because <see cref="Module{T}.GetAwaiter()"/>
+    /// returns <c>ModuleResult&lt;T?&gt;</c>, matching the nullable return type of ExecuteAsync.
+    /// </remarks>
     public static async Task AssertSuccessWithValue<T>(ModuleResult<T?> moduleResult)
         where T : class
     {
@@ -27,6 +31,10 @@ public static async Task AssertSuccessWithValue<T>(ModuleResult<T?> moduleResult
     /// Asserts that a module result represents a successful execution.
     /// Checks: ModuleResultType is Success, Exception is null.
     /// </summary>
+    /// <remarks>
+    /// The signature uses <c>ModuleResult&lt;T?&gt;</c> because <see cref="Module{T}.GetAwaiter()"/>
+    /// returns <c>ModuleResult&lt;T?&gt;</c>, matching the nullable return type of ExecuteAsync.
+    /// </remarks>
     public static async Task AssertSuccess<T>(ModuleResult<T?> moduleResult)
         where T : class
     {