Fix ddc brightness not applying because process exits before debounce timer runs (#2217)

* Fix ddc brightness not applying because process exits before debounce timer runs

* Added sync.WaitGroup to DDCBackend and use it instead of loop in wait logic, added timeout in case i2c hangs.

* go fmt

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Co-authored-by: bbedward <bbedward@gmail.com>

core/cmd/dms/commands_brightness.go

@@ -236,6 +236,7 @@ func runBrightnessSet(cmd *cobra.Command, args []string) {
 			defer ddc.Close()
 			time.Sleep(100 * time.Millisecond)
 			if err := ddc.SetBrightnessWithExponent(deviceID, percent, exponential, exponent, nil); err == nil {
+				ddc.WaitPending()
 				fmt.Printf("Set %s to %d%%\n", deviceID, percent)
 				return
 			}