v0.6.0

Added

• Added a shared in-memory WAL byte ring as the only append path. Foreground
  writers reserve byte ranges concurrently, copy encoded records directly into
  the ring, and a single flusher drains committed byte prefixes to the WAL file.
• Added loom coverage and crash-soak validation for the WAL ring's
  reserve/publish/flush ordering, including multi-publisher gap-safety checks.

Changed

• Flattened leaf storage and child addressing for the persistent ART layout:
  small records can stay inline, child body offsets are stored directly, and
  inner-node child scans use compact u16 addressing with SIMD fast paths.
• Reworked the WAL group-commit plumbing around ring backpressure instead of a
  per-record channel/worker handoff, reducing the concurrent durable write
  bottleneck while preserving the existing WAL record format and replay reader.
• Tightened journal validation so empty or over-capacity records are rejected
  before reservation instead of relying on debug-only assertions.

Removed

• Removed the legacy WAL channel backend and its transitional design documents.
  The ring-backed journal is now the only implementation.
• Removed rejected experiment notes that were no longer part of the supported
  architecture.

Validation

• cargo test --workspace --all-features --locked
• cargo clippy --workspace --all-features --all-targets --locked -- -D warnings
• RUSTFLAGS="--cfg loom" cargo test -p holt --lib journal::ring::loom --locked