refactor: Add more checks to pre-commit

Updated existing pre-commit hooks and added some new hooks:

- Remove trailing whitespace
- Ensure every non-empty file ends with a new line
- Check YAML file validity
- Prevent adding large files
- Ensure any scripts with shebangs are executable

Added a GitHub action to run pre-commit on every commit. Removed any
existing actions which duplicate pre-commit.

Ran pre-commit on the codebase.

app/boards/shields/elephant42/elephant42.keymap

@@ -3,7 +3,7 @@
  *
  * SPDX-License-Identifier: MIT
  */
- 
+
 #include <behaviors.dtsi>
 #include <dt-bindings/zmk/keys.h>
 #include <dt-bindings/zmk/bt.h>
@@ -19,7 +19,7 @@
 
     default_layer {
       bindings = <
-  &lt ADJT ESC  &kp Q &kp W &kp E     &kp R    &kp T                          &kp Y     &kp U    &kp I     &kp O   &kp P    &kp DEL 
+  &lt ADJT ESC  &kp Q &kp W &kp E     &kp R    &kp T                          &kp Y     &kp U    &kp I     &kp O   &kp P    &kp DEL
   &mt LCTRL TAB &kp A &kp S &kp D     &kp F    &kp G                          &kp H     &kp J    &kp K     &kp L   &kp SEMI &kp SQT
                 &kp Z &kp X &kp C     &kp V    &kp B                          &kp N     &kp M    &kp COMMA &kp DOT &kp FSLH
                             &kp LSHFT &mo LOWR &kp LGUI &kp BSPC    &kp SPACE &kp ENTER &mo RAIS &kp LALT