refactor(general): cleanup iomem hints (#5439)

- rename package to iomem
- update comments
- unexport `directoryWithOptions`
- check for `Close()` error on test cleanup
- reword flag description
- wrap errors to facilitate troubleshooting
- update logging message

cli/command_snapshot_create.go

@@ -78,7 +78,7 @@ func (c *commandSnapshotCreate) setup(svc appServices, parent commandParent) {
 	cmd.Flag("flush-per-source", "Flush writes at the end of each source").Hidden().BoolVar(&c.flushPerSource)
 	cmd.Flag("override-source", "Override the source of the snapshot.").StringVar(&c.sourceOverride)
 	cmd.Flag("send-snapshot-report", "Send a snapshot report notification using configured notification profiles").Default("true").BoolVar(&c.sendSnapshotReport)
-	cmd.Flag("hint-streaming-reads", "Release file memory after reading to reduce backup memory footprint (Linux only, best-effort).").
+	cmd.Flag("hint-streaming-reads", "[EXPERIMENTAL] Hint the OS to release memory used for I/O after reading files that are being backed up, aiming at reducing the memory footprint during backups (Linux only, best-effort).").
 		Default("false").Hidden().BoolVar(&c.snapshotCreateStreamingReads)
 
 	c.logDirDetail = -1