Add and expose metrics in ObjectStore Trait

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The current ObjectStore Trait and implementations do not collect and expose any metrics.
Add some metrics like read/write/delete ops counts, scan bytes, elapse times etc and expose them will be very useful
in the production environment.

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Start by locating the ObjectStore Trait and each of its implementations, then review how their read, write, delete, and scan operations are structured. Define the metric scope and exposure point with maintainers; done means the agreed operation counts, scanned bytes, and elapsed times are collected and accessible across the relevant implementations.

Written by the indexing model from the issue text.