[Excalidraw] Option to make laser drawings persistent

### Feature Request: Option to make laser drawings persistent (like iPad laser) **Description** Right now, when using the laser tool, the drawn line disappears automatically after a few seconds. It would be useful to have an **option to keep the laser visible until manually cleared or toggled off**. This would mimic the behavior of the iPad’s laser pointer, where users can choose between a temporary (disappearing) laser and a persistent one. --- **Why this is useful** - Allows presenters to highlight something for a longer time without it fading too quickly. - Gives users control over whether the laser is **temporary** (current behavior) or **persistent** (proposed option). - Makes it easier in teaching, demos, and collaborative sessions where emphasis needs to stay visible. --- **Suggested approach** - Add a toggle/checkbox in the laser tool menu: - *Temporary (default)* → laser disappears after a few seconds. - *Persistent* → laser remains on the canvas