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fix: Keyboard lost key-up bug - #2436
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Description of Changes
PS2Keyboard.cs (the core fix)
Added _pressedKeys — a HashSet tracking which keys the device believes are held.
EnqueueKeyEvent now adds/removes from the set (excluding the non-trackable None, Pause, PrintScreen).
Added ReleaseAllKeys() — emits a deterministic BREAK frame for each held key (sorted by enum order), then clears the set and resets the in-flight typematic repeat.
Wired _pressedKeys.Clear() + repeat reset into the buffer-overflow path in EnqueueScanCodeFrame, so a dropped key-up can't latch.
InputEventQueue.cs — added KeyboardDevice property and ReleaseAllKeys(), marshalled onto the emulator thread.
EmulatorMcpServices.cs — on pause (PauseHandler.Pausing), calls inputEventHub.ReleaseAllKeys().
MainWindowViewModel.cs / MainWindow.axaml.cs / Spice86DependencyInjection.cs — on window deactivation, calls inputEventHub.ReleaseAllKeys().
Rationale behind Changes
I fixed the lost-key-up bug by implementing a device-side release-all mechanism in the PS/2 keyboard, wired it to all three loss routes (window deactivation, pause, buffer overflow), and added tests. All new tests pass;
fixes #2407
Suggested Testing Steps
New file tests/Spice86.Tests/Emulator/Devices/Keyboard/PS2KeyboardReleaseAllKeysTests.cs (6 tests, all passing). The key engineering part was a controllable IEmulatedClock plus a drain helper that mimics what the guest does in INT9 (read 0x64, then 0x60), since the 8042's 0.3ms inter-byte delay and _waitingBytesFromKbd gating must be driven to observe the emitted scancodes.