Ensure our enumerations only use the size of a char

We are currently wasting a lot of space by writing enumerations as full
blown integers, where we could force them to have only 1 byte as we are
not using values bigger than 255.

Signed-off-by: Pablo Galindo <pablogsal@gmail.com>

src/memray/_memray/hooks.h

@@ -88,7 +88,7 @@ struct SymbolHook
 void
 ensureAllHooksAreValid();
 
-enum class Allocator {
+enum class Allocator : unsigned char {
     MALLOC = 1,
     FREE = 2,
     CALLOC = 3,