[Feature/Improvement] Add button to set all sound effects to None

**Purpose:** As a user, I would like to quickly program a timer with no sound effects.

**More details:**

When creating a timer, if a user would like all sound effects set to "None" then they must manually select each dropdown, and select "None". This is time consuming. There should be a button on the page to mute (set to None) all sounds.

Most likely use the [volume off material icon](https://fonts.google.com/icons?selected=Material+Symbols+Outlined:volume_off:FILL@0;wght@400;GRAD@0;opsz@24&icon.query=volume) for this.

**Acceptance Criteria:**
- Mute button added to the setSounds page.

在 Flutter 程式碼庫中尋找 setSounds 頁面，可能位於 lib/screens/ 中。找出用於音效的下拉式元件。新增一個帶有 volume_off 圖示的按鈕，按下時將所有下拉式元件的值設定為 'None'。在模擬器或裝置上執行應用程式，以測試此變更。

由索引模型根據 Issue 內容生成。