refactor slightly + add concepts & difficulty to the practice in config

config.json

@@ -200,9 +200,13 @@
         "slug": "rational-numbers",
         "name": "Rational Numbers",
         "uuid": "9858a357-b935-437d-b4e0-c3aac20859cf",
-        "practices": [],
+        "practices": [
+          "operator-overload",
+          "mutability",
+          "integers"
+        ],
         "prerequisites": [],
-        "difficulty": 1
+        "difficulty": 3
       }
     ],
     "foregone": [

exercises/practice/rational-numbers/.meta/example.cairo

@@ -86,8 +86,9 @@ impl RationalPow of RationalPowTrait {
         if *self.numer == 0 {
             return *self;
         };
-        // fast_power works only with unsigned integers
+
         let power_abs = abs(power);
+
         // determine the new number's sign
         let sign: i128 = if *self.numer < 0 && power_abs % 2 == 1 {
             -1
@@ -106,8 +107,8 @@ impl RationalPow of RationalPowTrait {
     }
 
     fn rpow(self: @u128, power: Rational) -> u128 {
-        // Cairo does not support floating point numbers, so a negative rational number
-        // will always return the result 0 (as 1 divided by any number is 0 in Cairo)
+        // Cairo only supports integers, so a negative rational exponent
+        // will always return the result 0
         if power.numer < 0 {
             return 0;
         };