init: Request SCHED_RR using CAP_SYS_NICE and add Python to nix dev shell (#2690)

* nix: add python3 to devShell

* init: request SCHED_RR scheduling policy

* init: checks if host supports reseting scheduler on fork

* init: make gainRealTime more compatible with other OSes

* init: remove linux-only code

src/main.cpp

@@ -89,6 +89,7 @@ int main(int argc, char** argv) {
     }
 
     std::cout << "Welcome to Hyprland!\n";
+    Init::gainRealTime();
 
     // let's init the compositor.
     // it initializes basic Wayland stuff in the constructor.