update to storybook 10

[CodeWitchBella]

Version 6 of this addon seems to work with storybook v10, but it generates warnings. This PR fixes that and performs related cleanup.

Main changes:

• bump storybook peer dependency in the published package
• drop cjs build

Other changes (since this is major version bump):

• change react peer dependency to match react-router's (>=18)
• update readme
• bump dependencies in top-level package.json and test package.json to allow testing the change
• fix vitest to work with the latest version (this was needed to get the esm-only working)

Finally, there are some weird things in package.json. I tried to remove what seemed unused but I wasn't sure what is needed (eg. the main and dist fields can probably be dropped altogether now that exports support is pretty good).

Anyway, cheers for awesome package :+1:

Proposed changelog

Support for storybook 10. Dropped cjs build of the package.

breaking: drop support for react < 18 (it probably didn't work before anyway)

Sidenote

Since this is bumping major version, it might make sense to skip a major and go straight to v7 and make v6 be the version which support react router v6 + latest storybook (I was reading some discussions on some recent tickets). But since I don't use v6, I have no big stakes in this.