fix a lot of low level cppcheck warnings (#9623)

* simplify the observer pattern, since all the called functions are const getters.
* use arduino macro over std: for numerical values and refactor local variables in drawScrollbar()
* oh, so Cppcheck actually complained about const pointers not being const.
* slowly getting out of ifdef hell
* fix inkHUD warnings as well
* last 2 check warnings
* git checks should fail on low defects from now on

variants/esp32c6/m5stack_unitc6l/platformio.ini

@@ -43,4 +43,4 @@ lib_ignore =
   NonBlockingRTTTL
   libpax
 build_src_filter = 
- ${esp32c6_base.build_src_filter} +<../variants/esp32c6/m5stack_unitc6l>
+ ${esp32c6_base.build_src_filter} +<../variants/esp32c6/m5stack_unitc6l>