ReerJSON 1.2.0

ReerJSON 1.2.0

• Adopt Swift 6.4-only performance optimizations across parsing, streaming, DOM traversal, sorted key writing, and integer array encoding.
• Add borrowed JSONDocument traversal APIs to reduce ARC traffic and avoid extra value copies in DOM-style access.
• Update yyjson to 0.13.0 and enable lowercase Unicode hex escaping so ReerJSON encoder output matches Foundation for control-character escapes.
• Update README documentation and SwiftPM dependency example for 1.2.0.