docs(audits): ReorderBuffer cache profiling strategy

[oferchen]

Summary

• Adds docs/audits/reorder-buffer-cache-strategy.md defining the perf-counter measurement plan for Add amd64 tarball artifact and guard packaging alternatives #1854 (companion to the existing static cache-behavior audit).
• Covers both engine::concurrent_delta::ReorderBuffer<T> (ring) and transfer::reorder_buffer::BoundedReorderBuffer<T> (BTreeMap), with cache-line layout analysis and false-sharing risk assessment.
• Defines the insert-pattern matrix (in-order / reverse / random / pathological) wired against the existing 10K-10M scaling bench at crates/engine/benches/reorder_buffer_scaling.rs, plus decision thresholds and layout-tuning hypotheses.

Test plan

• Doc-only change; no code paths touched.
• cargo fmt --all -- --check (CI).
• Markdown link / path references resolve against current source tree.