feat: add as type casting

tests/cast_float_to_int.test

@@ -0,0 +1,24 @@
+[code]
+fn cast_f32_to_i32(x: f32) -> i32 {
+    return x as i32;
+}
+
+fn cast_f64_to_u64(x: f64) -> u64 {
+    return x as u64;
+}
+
+[harness]
+#include <stdint.h>
+
+extern int32_t cast_f32_to_i32(float x);
+extern uint64_t cast_f64_to_u64(double x);
+
+int main() {
+    if (cast_f32_to_i32(3.14f) != 3) return 1;
+    if (cast_f32_to_i32(-2.9f) != -2) return 2;
+    if (cast_f64_to_u64(42.999) != 42) return 3;
+    return 0;
+}
+
+[expected_return_code]
+0