feat: add floats

tests/float_parsing.test

@@ -0,0 +1,17 @@
+[code]
+fn test_exponents() -> f64 {
+    let a: f64 = 1e3;
+    let b: f64 = 2.5e-1;
+    return a * b; // 1000.0 * 0.25 = 250.0
+}
+
+[harness]
+extern double test_exponents();
+
+int main() {
+    if (test_exponents() == 250.0) return 0;
+    return 1;
+}
+
+[expected_return_code]
+0