add rustfinity constant and primitive data solutions

Rust/rustifinity/challenges/constants.rs

@@ -0,0 +1,9 @@
+// Define a constant MAX_SIZE with a value of 100.
+// NOTE: Define the constant outside the main function
+// Your code here
+
+pub fn main() -> i32 {
+    MAX_SIZE
+}
+
+const MAX_SIZE : i32 = 100;

Rust/rustifinity/challenges/primitive-data-types.rs

@@ -0,0 +1,10 @@
+pub fn data_types() {
+    // 1. Define variable `x` of type `u8`
+    let x : u8;
+    // 2. Define variable `y` of type `f64`
+    let y : f64;
+    // 3. Define variable `z` of type `bool`
+    let z : bool;
+    // 4. Define variable `a` of type `char`
+    let a : char;
+}