Fixes React v19 incompatibility, increasing React minimum to v18

[lourd]

Description

This library is incompatible with React 19 because it's usage of ReactDOM.render which has been dropped in v19.

I've changed the usage of that to createRoot and increased the required react and react-dom versions to v18.

This will be a new major version as it is a breaking change to all users not on at least v18.

Testing

I tried running the tests but they were failing for me. They were failing before I made any changes with:

`Tooltip` must be used within `TooltipProvider`

After the changes they're failing with:

> Cannot read property 'useRef' of null

I think that means there's multiple versions of React being bundled, but I wasn't able to figure out how to debug that.