Add Undo Feature to Model Evaluation Process

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**Summary:**
As a user of FastChat, I've encountered a scenario where I've accidentally evaluated a model with no option to revert or cancel the action. This can be frustrating and potentially lead to wasted resources. I propose an enhancement to introduce an undo functionality for the model evaluation process.

**Problem:**
There is no current method to cancel or undo a model evaluation once the 'Evaluate' button has been clicked.

**Proposed Solution:**
Implement an undo option that provides a short time window (e.g., 5-10 seconds) after initiating a model evaluation during which a user can cancel the action. Only then the models could be displayed.

**Acceptance Criteria:**
- After clicking 'Evaluate', an 'Undo' button should appear for a predefined time window (suggestion: 5-10 seconds).
- If the 'Undo' button is clicked within this time frame, the evaluation process is stopped, and no data is recorded.
- If the time window elapses without the 'Undo' button being clicked, the model evaluation proceeds as normal.

**Potential Benefits:**
- Reduces the risk of accidental model evaluations.
- Provides users with a sense of control and flexibility.
- Improves user experience by preventing unnecessary frustrations.

No files, tests, or entry points are named. Start by locating the model evaluation UI and the existing Evaluate action, then determine how cancellation and recording are handled; done means an Undo control appears for the chosen window, stops evaluation without recording data, and otherwise preserves normal evaluation.

Written by the indexing model from the issue text.