[frontend] Slow and Turbo modes (#3525)

Closes #3344

Adds slow and turbo modes with configurable speeds that can then be
toggled by the user. Behavior is:
- Standard/slow limit, toggle turbo = turbo
- Turbo limit, toggle turbo = standard
- Standard/turbo limit, toggle slow = slow
- Slow limit, toggle slow = standard

Enabling the turbo/slow mode enables the frame limiter unconditionally.

This has some conflicts with VSync. For example when I set my refresh
rate to 60hz and enable vsync, turbo mode does nothing. Not sure how to
go about fixing this, @MaranBr probably knows better the proper
solution.

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3525
Reviewed-by: DraVee <dravee@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>

src/core/perf_stats.cpp

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 // SPDX-FileCopyrightText: 2017 Citra Emulator Project
@@ -143,7 +143,7 @@ void SpeedLimiter::DoSpeedLimiting(microseconds current_system_time_us) {
 
     auto now = Clock::now();
 
-    const double sleep_scale = Settings::values.speed_limit.GetValue() / 100.0;
+    const double sleep_scale = Settings::SpeedLimit() / 100.0;
 
     // Max lag caused by slow frames. Shouldn't be more than the length of a frame at the current
     // speed percent or it will clamp too much and prevent this from properly limiting to that