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/init/initHelpers.hpp

@@ -4,4 +4,5 @@
 
 namespace Init {
     bool isSudo();
+    void gainRealTime();
 };