Add yayl package

[golimpio]

Adds yayl (YAYL — Yet Another YAML Library) to the package index.

• What: A native-Zig YAML parser and emitter, converted from the MIT-licensed C library libfyaml. Full read/write support for block and flow collections, all scalar styles, anchors/aliases, tags, directives, and multi-document streams, plus a path-based document mutation API.
• Repo: https://github.com/npmonster/yayl (MIT, source root src/yaml.zig)
• Tests: 47 unit/integration tests green in Debug and ReleaseSafe with zero leaks.
• Name yayl is currently unclaimed in this index.

Tagged serialization. Happy to adjust anything the validation requires.