fix(server): return SQLite write versions atomically

[ericcurtin]

Summary

SQLite put_if returned the version of a later writer. Use RETURNING, as Postgres does.

Related Issue

Closes #4401

Changes

• RETURNING for version-checked updates and unconditional upserts.
• Shared write_result_from_row helper.
• Concurrent writer test.

Testing

• Checks appropriate to the affected code and behavior pass
• Unit tests added/updated (if applicable)
• E2E tests added/updated (if applicable)

cargo fmt, cargo clippy --all-targets and cargo test --lib for openshell-server. The new test fails (duplicate versions) without the change.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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[ericcurtin]

@johntmyers @elezar PTAL when you get a chance, and /ok to test b7b318366d882887c088b8a9b66de5632a13b7a2 if it looks good. Thank you!