Release v1.2.3

Changes

• Initialize reserved counters for local and shared-memory queues
• Validate shared-memory size is power-of-two and element size matches when attaching
• Add lossy semantics documentation and debug loss detection counter
• Add lossy overwrite tests for in-process and shared-memory queues
• Align hot atomics to cache lines and add light spin backoff under contention
• Add reserve(1) fast path using fetch_add
• Add SLICK_QUEUE_ENABLE_CPU_RELAX to control pause/yield backoff
• Guard against zero-length reservations
• Add limits header