chore(deps): support @netlify/blobs v8

[serhalp]

The peer dependency only specifies support for v6 and v7, but v8 works just fine.

Closes #485.

This adds v8 to the peer dependencies, bumps the dev dep to v8, updates the tests (there's a new requirement that's specific to unusual use cases like unstorage's tests, which are run outside of the Netlify platform and the Netlify CLI), and adjust the driver types to ensure compatibility with all supported versions.

See https://github.com/netlify/blobs/pull/183.

I believe @netlify/blobs@8 will error in local dev when using netlify-cli before 17.21.1. This doesn't seem like unstorage's problem though, so I didn't do anything about that here.