feat: add floats

tests/float_f64_arithmetic.test

@@ -0,0 +1,20 @@
+[code]
+fn test_f64(x: f64, y: f64) -> f64 {
+    let z: f64 = 2.5;
+    // (7.0 - 2.0) / 2.5 + (7.0 * 2.0) = 5.0 / 2.5 + 14.0 = 2.0 + 14.0 = 16.0
+    return (x - y) / z + (x * y);
+}
+
+[harness]
+extern double test_f64(double x, double y);
+
+int main() {
+    double result = test_f64(7.0, 2.0);
+    if (result == 16.0) {
+        return 0;
+    }
+    return 1;
+}
+
+[expected_return_code]
+0