Add a function for fetching the RTTIME limit

We can use this to more easily diagnose issues caused by PipeWire.

src/common/utils.cpp

@@ -48,6 +48,15 @@ bool set_realtime_priority(bool sched_fifo, int priority) noexcept {
                               &params) == 0;
 }
 
+std::optional<rlim_t> get_rttime_limit() noexcept {
+    rlimit limits{};
+    if (getrlimit(RLIMIT_RTTIME, &limits) == 0) {
+        return limits.rlim_cur;
+    } else {
+        return std::nullopt;
+    }
+}
+
 bool pid_running(pid_t pid) {
     // With regular individually hosted plugins we can simply check whether the
     // process is still running, however Boost.Process does not allow you to do