xla

dc5a7480 - Async RNG seed upload with env var `XLA_TRANSFER_SEED_ASYNC=1` (#3292) (#3393)

Async RNG seed upload with env var `XLA_TRANSFER_SEED_ASYNC=1` (#3292) (#3393) * Implement RNG seed Async upload * Fix review comments * Make RNG async controlled by an env var and add unit test