fix: stop spamming error logs for disks without block dev queue stats

not all devices have them. fixes errors such as this:

```
[root@testbox-arch /]# journalctl -ex -u mango.service --no-pager | grep -i 'no such'
Jul 28 18:52:50 testbox-arch mango[79]: {"time":"2024-07-28T18:52:50.862645518Z","level":"ERROR","msg":"Failed to get queue stats for block device","hostname":{"system":"testbox-arch","inventory":"testbox-arch"},"worker":"manager","manager":{"inventory":"/opt/mango/inventory","hostname":"testbox-arch","enrolled":true,"runID":"01J3XB0DSDX99FXHCJ79JM2HGE"},"metadata_collector":"storage","err":"open /sys/block/zram0/queue/nr_requests: no such file or directory","device":"zram0"}
Jul 28 18:52:52 testbox-arch mango[79]: {"time":"2024-07-28T18:52:52.922005911Z","level":"ERROR","msg":"Failed to get queue stats for block device","hostname":{"system":"testbox-arch","inventory":"testbox-arch"},"worker":"manager","manager":{"inventory":"/opt/mango/inventory","hostname":"testbox-arch","enrolled":true,"runID":"01J3XB0FSQ6BPT9FP6ZXMJ78GT"},"metadata_collector":"storage","err":"open /sys/block/zram0/queue/nr_requests: no such file or directory","device":"zram0"}
Jul 28 18:52:54 testbox-arch mango[79]: {"time":"2024-07-28T18:52:54.975231863Z","level":"ERROR","msg":"Failed to get queue stats for block device","hostname":{"system":"testbox-arch","inventory":"testbox-arch"},"worker":"manager","manager":{"inventory":"/opt/mango/inventory","hostname":"testbox-arch","enrolled":true,"runID":"01J3XB0HSWH4Y8BTAWD04T4875"},"metadata_collector":"storage","err":"open /sys/block/zram0/queue/rq_affinity: no such file or directory","device":"zram0"}
Jul 28 18:52:57 testbox-arch mango[79]: {"time":"2024-07-28T18:52:57.018631108Z","level":"ERROR","msg":"Failed to get queue stats for block device","hostname":{"system":"testbox-arch","inventory":"testbox-arch"},"worker":"manager","manager":{"inventory":"/opt/mango/inventory","hostname":"testbox-arch","enrolled":true,"runID":"01J3XB0KSQKTX1EK7MVDXT5VRB"},"metadata_collector":"storage","err":"open /sys/block/zram0/queue/rq_affinity: no such file or directory","device":"zram0"}
```

internal/manager/system_metadata.go

@@ -219,7 +219,8 @@ func getStorageMetadata(ctx context.Context, logger *slog.Logger) storageMetadat
 	for _, blockDev := range blockDevs {
 		blockDevPath := filepath.Join(blockDevDir, blockDev)
 		qStats, err := fs.SysBlockDeviceQueueStats(blockDev)
-		if err != nil {
+		// block dev queue stats may not exist for all devices
+		if err != nil && !os.IsNotExist(err) {
 			mdLogger.LogAttrs(
 				ctx,
 				slog.LevelError,