fix: keep panel restarts from hanging on the CPU job and Telegram (#7029)

Restarting the panel left it unreachable for up to a minute. CheckCpuJob sampled cpu.Percent over its whole one-minute period, so cron.Stop nearly always waited on it; it now diffs cpu.Times against its previous run (iowait counted as idle, as before). With Telegram unreachable, bus.Stop waited on an in-flight send and tgbot.Start ran getMe/setMyCommands inline; each bot call now returns once StopBot closes the bot's stop channel, the bot stops before the bus, and the artwork/commands warm-up runs in the background.

internal/util/sys/cpu_times.go

@@ -0,0 +1,36 @@
+package sys
+
+import "github.com/shirou/gopsutil/v4/cpu"
+
+// CPUBusyPercent is the busy share of CPU time between two cumulative samples,
+// counting iowait as busy; ok is false when no time elapsed or the counters reset.
+func CPUBusyPercent(prev, cur cpu.TimesStat) (percent float64, ok bool) {
+	return cpuPercent(prev, cur, true)
+}
+
+// CPUWorkPercent is CPUBusyPercent with iowait counted as idle, as gopsutil's
+// cpu.Percent does, so a host waiting on disk is not reported as CPU-bound.
+func CPUWorkPercent(prev, cur cpu.TimesStat) (percent float64, ok bool) {
+	return cpuPercent(prev, cur, false)
+}
+
+func cpuPercent(prev, cur cpu.TimesStat, iowaitIsBusy bool) (float64, bool) {
+	// Guest and GuestNice are already counted inside User and Nice on Linux.
+	idle := cur.Idle - prev.Idle
+	busy := (cur.User - prev.User) +
+		(cur.System - prev.System) +
+		(cur.Nice - prev.Nice) +
+		(cur.Irq - prev.Irq) +
+		(cur.Softirq - prev.Softirq) +
+		(cur.Steal - prev.Steal)
+	if iowait := cur.Iowait - prev.Iowait; iowaitIsBusy {
+		busy += iowait
+	} else {
+		idle += iowait
+	}
+	total := busy + idle
+	if total <= 0 {
+		return 0, false
+	}
+	return min(max(100*busy/total, 0), 100), true
+}