[[BP-62] Expose batchReadUnconfirmedAsync to ReadHandle

[dao-jun]

This is a supplement to BP62

Motivation

batchReadUnconfirmedAsync doesn't exposed to ReadHandle now, downstream projects maybe depend on the method.

Changes

1. Expose batchReadUnconfirmedAsync to ReadHandle
2. Add tests

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[eolivelli]

Overall the code change looks good

Please add unit tests about error scenarios (input validations, internal errors....)
errors must be reported accurately in the CompletableFuture

Also test the fallback case where batch reads are not available

[dao-jun]

@hangc0276 @lhotari @zymap PTAL

[eolivelli]

Patch looks good to me, as far as CI passes.
I have restarted the failed jobs

[dao-jun]

/bkbot rerun