ublk-azblob

ci(e2e): cache runner image (BuildKit/GHA) and cargo artifacts (#7)

Add NBD compatibility target and e2e test (#6)

Add unit and e2e coverage for writes through the file-based cache (#3)

Merge pull request #2 from tg123/fix-buffered-async-mutex

perf(buffered): never hold the state lock across inner I/O