fix: Toasts can be auto-dismissed when concurrent mode is enabled

[frankieyan]

Short description

This updates the Toast component so that its auto dismiss effect is compatible with new <StrictMode> behaviours in dev mode. As we can no longer assume effects are just run once, this removes the timeoutRunning state, reducing the reliance on the setupAutoDismiss effect and instead allow startTimeout to set the timeout directly.

Test plan

• Run storybook and navigate to http://localhost:6006/?path=/docs/design-system-toast--notification-toasts-story.
• Verify that toasts are dismissed after 10s
• Verify that hovering your mouse over the toasts prevents it from auto dismissing, and moving the cursor off restarts the timeout
• Optional: we can't test Reactist's storybook in React 18 without upgrading Storybook, so we can follow the instructions on using yelc to run this within Todoist, specifically this branch where we boot React with createRoot

Reference

https://react.dev/learn/synchronizing-with-effects#how-to-handle-the-effect-firing-twice-in-development

PR Checklist

• Added tests for bugs / new features
• Updated docs (storybooks, readme)
• Reviewed and approved Chromatic visual regression tests in CI