RootUtils: Interpret enums as signed integers in PyROOTInspector

I noticed this while I was debugging ATEAM-952. When we pythonize enum types, we don't actually look at the payload. Instead, we return the member's type name and name. Obviously, the type of an enum is the enum itself but for all practical purposes we might interpret them as integers (a la the debug messages) in this context. This way, we'll actually see what's stored. Let me explicitly tag @ssnyder to see what he thinks on this one.