chore: remove unused DeepSize trait and all implementations

[detail-app]

Removes the DeepSize trait (defined in common/src/deep_size.rs) and all impl DeepSize blocks across s2-common and s2-storage. The trait computed recursive byte-sizes of record types.

The sole production call-site was envelope.headers().deep_size() inside MeteredSize for Record, which was replaced in #349 with a cached HeaderSizing approach. Since then, the entire DeepSize call graph has had no production entry point — every impl DeepSize block only delegates to other impl DeepSize blocks that are themselves never invoked from outside.

History

• Last materially changed April 2026 (feat: request-time data encryption #349 @infiniteregrets)

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[greptile-apps]

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[infiniteregrets]

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