Refactor/dos console driver (#2095)

* refactor: console device based in FreeDOS

* feat: INT 16h/21h input: stuffahead buffer, DSR, key mapping

Added INT 16h AH=05h (Store Keystroke) support and refactored input handling to use a device-level stuffahead buffer for synthesized input (e.g., DSR responses), matching NANSI priority and bypassing key reassignment. ConsoleDevice now flushes both stuffahead and BIOS keyboard buffers. Improved extended key and backspace handling. ESC[0p now installs the default Ctrl+PrintScreen→Ctrl+P mapping. Added integration tests for key reassignment, buffer flushing, and DSR response correctness.

* feat: Add NANSI mode 99 and 43 handling to AnsiSequenceHandler

Implemented support for NANSI-specific modes in SetResetMode:
- Mode 99 toggles pseudo cursor behavior via _vga.CursorEmulation.
- Mode 43 reinitializes text mode, loads 8x8 font for 80x43 layout, sets cursor shape, and homes the cursor.

* fix: StoreKeystroke actually updates the Carry Flag on success and error

* refactor: combined if statements

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

* Fix review comments: echo stuffahead, backspace underflow, unused param, doc comments

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Co-authored-by: maximilien-noal <1087524+maximilien-noal@users.noreply.github.com>

---------

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: maximilien-noal <1087524+maximilien-noal@users.noreply.github.com>

Author: 3 people

src/Spice86.Core/Emulator/InterruptHandlers/Dos/DosInt21Handler.cs

@@ -724,6 +724,8 @@ public void ClearKeyboardBufferAndInvokeKeyboardFunction() {
             LoggerService.Debug("CLEAR KEYBOARD AND CALL INT 21 {Operation}", operation);
         }
         _keyboardInt16Handler.FlushKeyboardBuffer();
+        // NANSI dosfn7: also clears all device-level stuffahead buffers.
+        _dosFileManager.Stdin?.Flush();
         if (operation is not 0x0 and not 0x6 and not 0x7 and not 0x8 and not 0xA) {
             return;
         }

src/Spice86.Core/Emulator/InterruptHandlers/Input/Keyboard/KeyboardInt16Handler.cs

@@ -48,6 +48,7 @@ private void FillDispatchTable() {
         AddAction(0x01, () => GetKeystrokeStatus(true));
         AddAction(0x02, GetShiftFlags);
         AddAction(0x03, SetTypematicRateAndDelay);
+        AddAction(0x05, () => StoreKeystroke(true));
         AddAction(0x10, GetEnhancedKeystroke);
         AddAction(0x11, () => GetEnhancedKeystrokeStatus(true));
         AddAction(0x1D, () => Unsupported(0x1D));
@@ -243,6 +244,26 @@ public void GetShiftFlags() {
         State.AL = _biosDataArea.KeyboardStatusFlag;
     }
 
+    /// <summary>
+    /// INT 16h, AH=05h - Store Keystroke in keyboard buffer.
+    /// Writes the key code in CX (CH=scan code, CL=ASCII character) into the
+    /// BIOS keyboard buffer. On success AL=0, CF=0; if the buffer is full, AL=1, CF=1.
+    /// </summary>
+    public void StoreKeystroke(bool calledFromVm) {
+        ushort keyCode = State.CX;
+        if (LoggerService.IsEnabled(LogEventLevel.Verbose)) {
+            LoggerService.Verbose("STORE KEYSTROKE {KeyCode}", keyCode);
+        }
+        bool enqueued = _biosKeyboardBuffer.EnqueueKeyCode(keyCode);
+        State.AL = enqueued ? (byte)0 : (byte)1;
+        if(enqueued) {
+            SetCarryFlag(false, calledFromVm);
+        }
+        else {
+            SetCarryFlag(true, calledFromVm);
+        }
+    }
+
     /// <summary>
     /// Tries to get the pending keycode from the BIOS keyboard buffer without removing it.
     /// </summary>