Try parallelizing directory_get_entries with an async swh-storage client

Currently, the vault fetches directories one by one, loading them in parallel may speed up the process.

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Migrated from T3731 (view on Phabricator)

assigned to @vlorentz

marked this issue as related to swh/meta#3504

added Vault priority:Normal labels

Making an async swh-storage (or RPC client for our framework, in general) turns out the not be worth it, threads are just as efficient and don't require complex hacks

closed