[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/core_timing.cpp

@@ -201,7 +201,7 @@ u64 CoreTiming::GetClockTicks() const {
 
      if (Settings::values.sync_core_speed.GetValue()) {
          const auto ticks = double(fres);
-         const auto speed_limit = double(Settings::values.speed_limit.GetValue())*0.01;
+         const auto speed_limit = double(Settings::SpeedLimit())*0.01;
          return u64(ticks/speed_limit);
      } else {
          return fres;

src/core/hle/service/vi/conductor.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: Copyright 2024 yuzu Emulator Project
@@ -95,7 +95,7 @@ s64 Conductor::GetNextTicks() const {
         if (settings.use_speed_limit.GetValue()) {
             // Scales the speed based on speed_limit setting on MC. SC is handled by
             // SpeedLimiter::DoSpeedLimiting.
-            speed_scale = 100.f / settings.speed_limit.GetValue();
+            speed_scale = 100.f / Settings::SpeedLimit();
         } else {
             // Run at unlocked framerate.
             speed_scale = 0.01f;

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