fix(graphcache): Mark deferred, uncached results as partial

[kitten]

Resolves #3161

Summary

Previously, as hasNext wasn't consistently handled across the urql codebase prior to v4, we didn't have a signal and logic to handle partial, deferred results. We can now add the hasNext flag to @urql/exchange-graphcache and let deferred, uncached results fall through the usual cached result handling, and instead, pass the query on to the API.

Set of changes

• Add hasNext flag to cached query results
• Handle hasNext cache results in cacheExchange and pass them on
• Increase consistency of stale flag for cache-only operations