feat: add as type casting

tests/cast_float_to_float.test

@@ -0,0 +1,21 @@
+[code]
+fn promote_f32_to_f64(x: f32) -> f64 {
+    return x as f64;
+}
+
+fn demote_f64_to_f32(x: f64) -> f32 {
+    return x as f32;
+}
+
+[harness]
+extern double promote_f32_to_f64(float x);
+extern float demote_f64_to_f32(double x);
+
+int main() {
+    if (promote_f32_to_f64(3.5f) != 3.5) return 1;
+    if (demote_f64_to_f32(2.25) != 2.25f) return 2;
+    return 0;
+}
+
+[expected_return_code]
+0

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

tests/cast_int_to_float.test

@@ -0,0 +1,24 @@
+[code]
+fn cast_i32_to_f32(x: i32) -> f32 {
+    return x as f32;
+}
+
+fn cast_u64_to_f64(x: u64) -> f64 {
+    return x as f64;
+}
+
+[harness]
+#include <stdint.h>
+
+extern float cast_i32_to_f32(int32_t x);
+extern double cast_u64_to_f64(uint64_t x);
+
+int main() {
+    if (cast_i32_to_f32(42) != 42.0f) return 1;
+    if (cast_i32_to_f32(-10) != -10.0f) return 2;
+    if (cast_u64_to_f64(1337) != 1337.0) return 3;
+    return 0;
+}
+
+[expected_return_code]
+0

tests/cast_int_to_int.test

@@ -0,0 +1,23 @@
+[code]
+fn truncate_i32_to_i8(x: i32) -> i8 {
+    return x as i8;
+}
+
+fn extend_u8_to_i32(x: u8) -> i32 {
+    return x as i32;
+}
+
+[harness]
+#include <stdint.h>
+
+extern int8_t truncate_i32_to_i8(int32_t x);
+extern int32_t extend_u8_to_i32(uint8_t x);
+
+int main() {
+    if (truncate_i32_to_i8(257) != 1) return 1; // 257 = 0x0101, truncated to 8 bits is 0x01
+    if (extend_u8_to_i32(255) != 255) return 2;
+    return 0;
+}
+
+[expected_return_code]
+0