refactor: Fixes for soft-off based on review.

* Better naming for gpio-key behavior triggers.
* Tweaks to scanned behavior trigger to avoid bad semaphore use,
  and reduce chance of issues with slowly scanned matrixes.
* Various code cleanups of style issues.

app/dts/behaviors/soft_off.dtsi

@@ -8,7 +8,6 @@
     behaviors {
         /omit-if-no-ref/ soft_off: soft_off {
             compatible = "zmk,behavior-soft-off";
-            label = "SOFTOFF";
             #binding-cells = <0>;
         };
     };