Fixes #4456 - Clear MouseGrabView in App.End (#4460)

* Fixed MouseGrabView bug.

Added extensive test coverage for `Keyboard`, `Mouse`, `Timeout`, and `Popover` functionalities, including edge cases and concurrent access. Introduced parameterized and data-driven tests to reduce redundancy and improve clarity.

Refactored codebase for modularity and maintainability,
introducing new namespaces and reorganizing classes. Enhanced `MouseImpl`, `KeyboardImpl`, and `Runnable` implementations with improved event handling, thread safety, and support for the Terminal.Gui Cancellable Work Pattern (CWP).

Removed deprecated code and legacy tests, such as `LogarithmicTimeout` and `SmoothAcceleratingTimeout`. Fixed bugs related to mouse grabbing during drag operations and unbalanced `ApplicationImpl.Begin/End` calls. Improved documentation and code readability with modern C# features.

* Code cleanup.

* Update Tests/UnitTestsParallelizable/Application/Runnable/RunnableIntegrationTests.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Improve null handling and simplify test setup

In `MouseImpl.cs`, added an early `return` after the `UngrabMouse()`
call within the `if (view is null)` block to prevent further execution
when `view` is `null`, improving null reference handling.

In `RunnableIntegrationTests.cs`, removed the initialization of the
`IApplication` object (`app`) from the `MultipleRunnables_IndependentResults`
test method, simplifying the test setup and focusing on runnable behavior.

* Code cleanup

* API doc link cleanup

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Tests/UnitTests/View/Mouse/MouseTests.cs

@@ -49,8 +49,10 @@ public class MouseTests : TestsAllViews
 
         Application.RaiseMouseEvent (new () { ScreenPosition = new (xy + 1, xy + 1), Flags = MouseFlags.Button1Pressed | MouseFlags.ReportMousePosition });
         AutoInitShutdownAttribute.RunIteration ();
-
         Assert.Equal (expectedMoved, new Point (5, 5) == testView.Frame.Location);
+        // The above grabbed the mouse. Need to ungrab.
+        Application.Mouse.UngrabMouse ();
+
         top.Dispose ();
     }
 

Tests/UnitTests/View/ViewCommandTests.cs

@@ -152,6 +152,9 @@ public class ViewCommandTests
         Assert.Equal (1, btnAcceptedCount);
         Assert.Equal (0, wAcceptedCount);
 
+        // The above grabbed the mouse. Need to ungrab.
+        Application.Mouse.UngrabMouse ();
+
         w.Dispose ();
         Application.ResetState (true);
     }