iOS: one settings reload per save, not one per field

Pressing Save in the per-game panel produced seventy-one "Applying settings"
cycles, twice over in the logs from the disc bug. Each per-game setter writes
its one key and then queues a full reload, so a panel that writes every field
it owns gets a reload per field. Each of those re-reads the INI, re-runs the
GameDB fixups and rebuilds the GS config, which is most of why saving anything
took a visible moment.

The reload is now coalesced: a write schedules one shortly after, and if
another write lands first it hands the job over, so the last write in a burst
is the one that reloads. Seventy-one becomes one.

Left the reload in the bridge rather than adding a begin/end batch for the
panel to bracket its save with. The disc bug next door happened because a
caller did not know a rule it was supposed to follow, and a bracket is the same
shape: anything added later that forgets to wrap goes quietly back to the old
behaviour. This way there is no rule to remember.

The cost is that a change now applies about fifty milliseconds after the last
write instead of immediately, and if the app is backgrounded inside that window
the live apply is skipped, though the file is already written so it lands on the
next boot. Neither is noticeable for settings UI.

Only the ForCurrentGame setters are touched. The forISO ones never reloaded;
they exist precisely to write the file without applying it.

platforms/ios/app/src/main/cpp/ARMSX2Bridge.mm

@@ -62,6 +62,7 @@ extern "C" void ARMSX2_iOSCopyDeviceStats(int* outBatteryPercent, int* outTherma
 
 #include <algorithm>
 #include <array>
+#include <atomic>
 #include <cctype>
 #include <cmath>
 #include <cstdio>
@@ -3973,6 +3974,30 @@ extern "C" void ARMSX2_CaptureGraphicsHackState(void)
     return si.GetBoolValue(section.UTF8String, key.UTF8String, def);
 }
 
+// The per-game panel writes every field it owns when you press Save, and each write
+// used to queue a reload of its own. One tap came out the other side as seventy-odd
+// full config reloads, each re-reading the INI, re-running GameDB and rebuilding the
+// GS config. Let the last write in a burst be the one that reloads.
+static void ARMSX2RequestPerGameSettingsReload()
+{
+    static std::atomic<uint64_t> s_generation{0};
+    const uint64_t mine = s_generation.fetch_add(1, std::memory_order_relaxed) + 1;
+
+    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, static_cast<int64_t>(0.05 * NSEC_PER_SEC)),
+        dispatch_get_main_queue(), ^{
+            // Someone wrote after us, so they own the reload.
+            if (s_generation.load(std::memory_order_relaxed) != mine)
+                return;
+
+            // EmuConfig and the MTGS ring are the CPU thread's; this runs on the UI thread.
+            Host::RunOnCPUThread([]() {
+                VMManager::ReloadGameSettings();
+                if (MTGS::IsOpen())
+                    MTGS::ApplySettings();
+            });
+        });
+}
+
 + (void)setPerGameINIInt:(nonnull NSString *)section key:(nonnull NSString *)key value:(int)value forISO:(nonnull NSString *)isoName {
     std::string serial;
     u32 crc = 0;
@@ -4054,12 +4079,7 @@ extern "C" void ARMSX2_CaptureGraphicsHackState(void)
     si.SetIntValue(section.UTF8String, key.UTF8String, value);
     Error error;
     si.Save(&error);
-    // EmuConfig and the MTGS ring are the CPU thread's; this runs on the UI thread.
-    Host::RunOnCPUThread([]() {
-        VMManager::ReloadGameSettings();
-        if (MTGS::IsOpen())
-            MTGS::ApplySettings();
-    });
+    ARMSX2RequestPerGameSettingsReload();
 }
 
 + (void)setPerGameINIBoolForCurrentGame:(nonnull NSString *)section key:(nonnull NSString *)key value:(BOOL)value {
@@ -4072,12 +4092,7 @@ extern "C" void ARMSX2_CaptureGraphicsHackState(void)
     si.SetBoolValue(section.UTF8String, key.UTF8String, value);
     Error error;
     si.Save(&error);
-    // EmuConfig and the MTGS ring are the CPU thread's; this runs on the UI thread.
-    Host::RunOnCPUThread([]() {
-        VMManager::ReloadGameSettings();
-        if (MTGS::IsOpen())
-            MTGS::ApplySettings();
-    });
+    ARMSX2RequestPerGameSettingsReload();
 }
 
 + (float)getPerGameINIFloat:(nonnull NSString *)section key:(nonnull NSString *)key defaultValue:(float)def forISO:(nonnull NSString *)isoName {
@@ -4124,12 +4139,7 @@ extern "C" void ARMSX2_CaptureGraphicsHackState(void)
     si.SetFloatValue(section.UTF8String, key.UTF8String, value);
     Error error;
     si.Save(&error);
-    // EmuConfig and the MTGS ring are the CPU thread's; this runs on the UI thread.
-    Host::RunOnCPUThread([]() {
-        VMManager::ReloadGameSettings();
-        if (MTGS::IsOpen())
-            MTGS::ApplySettings();
-    });
+    ARMSX2RequestPerGameSettingsReload();
 }
 
 + (void)deletePerGameINIValueForCurrentGame:(nonnull NSString *)section key:(nonnull NSString *)key {
@@ -4144,12 +4154,7 @@ extern "C" void ARMSX2_CaptureGraphicsHackState(void)
     si.RemoveEmptySections();
     Error error;
     si.Save(&error);
-    // EmuConfig and the MTGS ring are the CPU thread's; this runs on the UI thread.
-    Host::RunOnCPUThread([]() {
-        VMManager::ReloadGameSettings();
-        if (MTGS::IsOpen())
-            MTGS::ApplySettings();
-    });
+    ARMSX2RequestPerGameSettingsReload();
 }
 
 + (nonnull NSString *)perGameIdentityKeyForCurrentGame {