widmogrod/mkunion

AI Summary: Create a comprehensive tutorial documenting how to use the `mkunion` Go library to build state machines. This includes creating a new documentation file, writing code examples demonstrating state modeling, transition functions, dependency injection, testing, and error handling, and updating existing documentation to link to the new tutorial. The tutorial should cover basic concepts and best practices, and ideally generate Mermaid diagrams for visualization.

AI Summary: The task involves creating comprehensive API documentation for several Go packages within the `x/` directory of the MkUnion project. This includes creating individual documentation files for each package, outlining their purpose, key concepts, API references with examples, and integration guides. The documentation should also highlight inter-package relationships and API stability. Finally, the main documentation needs updating to include links to the new `x/` package documentation.