[Bug]: Calling start() multiple times on a macos timer doesn't stop the previous timer #29076

Bug summary

When calling timer.start(); timer.start() on an already running timer, the previous timer should be stopped before starting a new one. On the macosx backend this causes two timers to be running under the hood.

Code for reproduction

import time
import matplotlib.pyplot as plt

timer = plt.figure().canvas.new_timer(interval=1000)

timer.add_callback(lambda: print(f"{time.ctime()}"))
timer.start()
timer.start()

plt.pause(2)

Actual outcome

4 prints, 2 per second

Tue Nov  5 09:07:27 2024
Tue Nov  5 09:07:27 2024
Tue Nov  5 09:07:28 2024
Tue Nov  5 09:07:28 2024

Expected outcome

2 prints, 1 per second

Tue Nov  5 09:07:27 2024
Tue Nov  5 09:07:28 2024

Additional information

No response

Operating system

macos

Matplotlib Version

main

Matplotlib Backend

macosx

Python version

No response

Jupyter version

No response

Installation

None