fix: stabilize concurrent mutation tests

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Summary

• return typed row-state errors instead of panicking when delete races lock-free insert publication
• preserve composite primary-key declaration order through code generation instead of randomizing it through a HashMap
• close and join persisted tuple-key tables before immediately reopening their files
• retain a strongly adversarial same-key stress test while bounding it independently of runner speed

Regression coverage

• worktable::upsert::raw_insert_delete_churn_never_panics_or_stalls
• persistence::tuple_primary_key::composite_primary_key_survives_mutations_and_reload
• worktable::tests::composite_primary_key_codegen_preserves_declaration_order
• worktable::upsert::upsert_completes_under_extreme_same_key_churn

Verification

• cargo fmt --all -- --check
• cargo test --workspace --all-targets
• cargo test --workspace --all-targets --features versioned-row-publication
• cargo test --workspace --all-targets --all-features
• cargo clippy --workspace --all-targets --all-features -- -D warnings

[pathscale]

Superseded by #46 (consolidated v1-blocker PR). Commit stabilize-concurrent-mutation-tests carried over as 3c248fd.