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

src/mesh/aes-ccm.cpp

@@ -33,7 +33,7 @@ static int constant_time_compare(const void *a_, const void *b_, size_t len)
         d |= (a[i] ^ b[i]);
     }
     /* Constant time bit arithmetic to convert d > 0 to -1 and d = 0 to 0. */
-    return (1 & ((d - 1) >> 8)) - 1;
+    return (1 & (((unsigned int)d - 1) >> 8)) - 1;
 }
 
 static void WPA_PUT_BE16(uint8_t *a, uint16_t val)