Investigate memory management issue with HttpRequest URLs in http_client.zig

Review and refactor how memory is managed for HttpRequest URLs, particularly in test scenarios where the deinit method tries to free global strings. Consider alternative approaches for test setups or memory management.

Reference:
```zig
// TODO: The request de-allocates the memory used by the url in the deinit method.
// Because of this, with this test, we have to dupe it or else it cant deinit a global string.
// Needing to do this is a sign that something is off here, but also newing up requests directly
// isn't really intended either. Either way, need to look into this further.
```

從 http_client.zig 開始，追蹤 HttpRequest URL 在初始化和 deinit 過程中的所有權，然後檢查所參照的測試設定。確定全域字串的處理方式，以及現有的重複解決方案是否仍然需要。完成的標準是請求清理不再嘗試釋放不屬於它的全域字串，且受影響的測試通過。

由索引模型根據 Issue 內容生成。