[ntuple] Add optimized bulk read of fixed-size arrays

[jblomer]

Explain what you would like to see improved and how.

The RArrayField should provide an optimized ReadBulkImpl, at least for simple types. That would allow bulk-reading of fixed-size arrays without the mask evaluation. Requested by ALICE.

ROOT version

master

Installation method

n/a

Operating system

n/a

Additional context

No response