Preventing non-return on non-void; changing printf format

[Zacharyprime]

Preventing non-return on non-void function:

/home/zachary/libwallaby/module/graphics/src/graphics.cpp: In function ‘PixelToaster::Pixel fromTrueColor(Encoding, int, int, int)’:
/home/zachary/libwallaby/module/graphics/src/graphics.cpp:139:1: warning: control reaches end of non-void function [-Wreturn-type]
  139 | }
      | ^

The compiler is unaware that there are only two valid inputs for the definition Encoding.
Changing the bottom case to default shouldn't change anything functionally since BGR and RGB are the only valid encodings.

Changing printf %d to %lu for long unsigned int:
This throws a warning because %d is not the correct printf syntax for long unsigned ints.
%lu matches the C++ docs and removes the warning.

[Zacharyprime]

The two most recent commits remove 2 warnings:
-Switching char to const char: Removes the warning of converting string to uint8_t (char*). It seems this is always used in the form of passing a constant expression and not an actual char pointer.

-Specify narrowing conversion: The compiler warns that the conversion is narrowing, this conversion's intention is to narrow into a lower bit representation so we add an explicit cast to tell the compiler that it is intentional.