Simplified register usage visualization

src/core/PrintInstructions.go

@@ -37,9 +37,9 @@ func (f *Function) PrintInstructions() {
 
 		for _, reg := range f.CPU.All {
 			if used&(1<<reg) != 0 {
-				registers.WriteString("⬤ ")
+				registers.WriteString("⏺ ")
 			} else {
-				registers.WriteString("◯ ")
+				registers.WriteString("  ")
 			}
 		}