Huge refactor: Make Core a singleton

src/backend/Scheduler.cpp

@@ -1,6 +1,5 @@
 #include <Scheduler.hpp>
-#include <core/Mem.hpp>
-#include <core/registers/Registers.hpp>
+#include <Core.hpp>
 
 void Scheduler::EnqueueRelative(const u64 t, const EventType type) { EnqueueAbsolute(t + ticks, type); }
 
@@ -19,7 +18,9 @@ u64 Scheduler::Remove(const EventType eventType) const {
   return 0;
 }
 
-void Scheduler::Tick(const u64 t, n64::Mem &mem) {
+void Scheduler::Tick(const u64 t) {
+  n64::Core& core = n64::Core::GetInstance();
+  n64::Mem& mem = core.cpu->GetMem();
   ticks += t;
   n64::MI &mi = mem.mmio.mi;
   n64::SI &si = mem.mmio.si;