Replace versioned.Value with a part.Map as the solution for providing a transactional view on the selector cache for any given SelectorPolicy. Avoid most of the part.Map index update overhead by reusing the same transaction for the policy update. Addition of new selectors to the selector cache are pooled into a single write transaction. Whenever the changes need to be observable via CachedSelector.GetSelections[At](), the updater must call the new SelectorCache.Commit() function.

Some interfaces that called for a version handle were always used with the special latest version handle. StateDB does not have a similar concept, so we have removed the version handle from the following interface functions:

• CachedSelector.GetSelections()
  • a new GetSelectionsAt() is added for explicit version access
• CachedSelector.Selects()
• DNSProxier.GetRules()

CachedSelector.Selects() and DNSProxier.GetRules() were always called with the static "latest version" handle, and most CachedSelector.GetSelections() calls in test code did the same. Implementations of these now internally get a read transaction on the latest version and access the selectors with that.

The main benefit of this change is the removal of pkg/container/versioned, that had an arcane API. This commit is the minimal change to achieve removal of pkg/container/versioned, with room for improvements like:

• Consider using statedb, using statedb indexes for namespace indexing
• Add CIDR indexing for (non-namespaced) CIDR selectors
• Explore using part.Set for storing the selections instead of a read-only slice. This would likely save some on updates, but would cost more on iteration.