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.cpp

@@ -3,3 +3,19 @@
 bool Init::isSudo() {
     return getuid() != geteuid() || !geteuid();
 }
+
+void Init::gainRealTime() {
+    const int                minPrio = sched_get_priority_min(SCHED_RR);
+    const struct sched_param param   = {.sched_priority = minPrio};
+
+    if (pthread_setschedparam(pthread_self(), SCHED_RR, &param)) {
+        Debug::log(WARN, "Failed to change process scheduling strategy");
+        return;
+    }
+
+    pthread_atfork(NULL, NULL, []() {
+        const struct sched_param param = {.sched_priority = 0};
+        if (pthread_setschedparam(pthread_self(), SCHED_OTHER, &param))
+            Debug::log(WARN, "Failed to reset process scheduling strategy");
+    });
+}