remove possibility of nil allocs from CSI volume/plugin

[tgross]

CSI volumes have references to allocations that get "denormalized" when we read them out of the state store. This has been a bug farm for us whenever we run into allocations that have been GC'd, and we've had to play wack-a-mole to fix this category of bug. The best way to do this is probably to avoid reading WriteAllocs and ReadAllocs at all at the server and treat it only as a value to send back to the CLI/UI, keeping the values of interest in WriteClaims and ReadClaims.

cc @langmartin for your thoughts

[tgross]

This issue has been worked over in #10927 and patched with #11890 #11932 #11931 #11892. We'll be issuing a patch release shortly for that fix. I'm going to close this issue.

Follow from #10927 (comment) for more information.

[github-actions]

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