fix(issue-324): Re-Hydrate upon remounting after unmounting

[fras2560]

Closes #324

[fras2560]

This change seems to address the issue I was running into.

I was not able to create a simplified repo but can do if you share a template to use for isolating the problem.

[fras2560]

@fongandrew any help with maybe moving this forward?

[fongandrew]

For future me (or anyone else digging through this), this happens because of how React's <StrictMode> works in development:

When Strict Mode is on, React will also run one extra setup+cleanup cycle in development for every Effect. This may feel surprising, but it helps reveal subtle bugs that are hard to catch manually.

The expectation in prod is that an unmount is a real unmount (i.e. the class instance is discarded) but in dev with StrictMode, React is doing stuff to detect imperative side effects.