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.dtsi

@@ -3,7 +3,7 @@
  *
  * SPDX-License-Identifier: MIT
  */
- 
+
 #include <dt-bindings/zmk/matrix_transform.h>
 
 / {
@@ -36,7 +36,7 @@ RC(1,0) RC(1,1) RC(1,2) RC(1,3) RC(1,4) RC(1,5)                 RC(1,6) RC(1,7)
             , <&pro_micro 7 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>
             ;
 
-    }; 
+    };
 };
 
 &pro_micro_i2c {