Serialization: refactor subarray and stats.

[KiterLuc]

*** Note: for now this is just a support PR to help designing the new code standard for the serialization codebase. ***

This change refactors the subarray and stats class to follow the new standard for the serialization code base.

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TYPE: IMPROVEMENT DESC: Serialization: refactor subarray and stats.

[shortcut-integration[bot]]

This pull request has been linked to Shortcut Story #19496: Write design document for new serialization code..