fix: synchronize CPU resource metrics reads

Hold resourceMetricsMapMu.RLock while the v3 CPU collector reads both the
subsystem map and its nested idle/iowait metrics. The unsynchronized reads
were inherited from upstream commit f7b665347 (minio/minio#19560).

Add value and concurrent Prometheus Gather regression tests, run them in
the targeted race CI job, and record the existing CPU metric names in the
compatibility inventory.

Fixes #210

Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/metrics-v3-system-cpu.go

@@ -69,6 +69,8 @@ func loadCPUMetrics(ctx context.Context, m MetricValues, c *metricsCache) error
 
 	// metrics-resource.go runs a job to collect resource metrics including their Avg values and
 	// stores them in resourceMetricsMap. We can use it to get the Avg values of CPU idle and IOWait.
+	resourceMetricsMapMu.RLock()
+	defer resourceMetricsMapMu.RUnlock()
 	cpuResourceMetrics, found := resourceMetricsMap[cpuSubsystem]
 	if found {
 		if cpuIdleMetric, ok := cpuResourceMetrics[getResourceKey(cpuIdle, nil)]; ok {