perf: f64 转字符串去中间分配并加整数 double 快路径

crates/oxide_builtins/src/json.rs

@@ -302,7 +302,7 @@ fn jsvalue_to_json<H: VmHost>(
         if !n.is_finite() {
             out.push_str("null");
         } else {
-            out.push_str(&oxide_runtime_api::js_number_to_string(n));
+            oxide_runtime_api::write_number_into(n, out);
         }
     } else if val.is_string() {
         let s = unsafe { (*val.as_string_ptr()).to_owned_string() };

crates/oxide_builtins/src/number.rs

@@ -181,7 +181,7 @@ pub fn number_to_string<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
     };
 
     if radix == 10 {
-        return NativeResult::Ok(vm.new_string(&oxide_runtime_api::js_number_to_string(n)));
+        return NativeResult::Ok(vm.new_string_owned(oxide_runtime_api::js_number_to_string(n)));
     }
 
     if n.is_nan() {
@@ -192,7 +192,7 @@ pub fn number_to_string<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
     }
     if n.abs() >= u128::MAX as f64 {
         // 超出 u128 可精确表示的整数范围，退化为十进制近似。
-        return NativeResult::Ok(vm.new_string(&oxide_runtime_api::js_number_to_string(n)));
+        return NativeResult::Ok(vm.new_string_owned(oxide_runtime_api::js_number_to_string(n)));
     }
     let neg = n.is_sign_negative();
     let mut value = n.abs().trunc() as u128;