Tailwind Variant v3

The `tailwind-variant-v3` package is a runtime variant utility specifically designed for Tailwind CSS v3, offering a TypeScript-first approach for defining and managing UI component styles. It is part of the `weapp-tailwindcss` monorepo, which integrates Tailwind CSS into WeChat Mini Programs and similar environments. The current stable version is `0.2.1`. Key features include composable variants (supporting `base`, `slots`, `variants`, `compoundVariants`, `compoundSlots`), responsive variant definitions, and deep integration with `tailwind-merge` for robust class name collision resolution. It provides `cn` and `cnBase` utilities and allows for custom `twMergeConfig` and pluggable `twMergeAdapter` implementations for alternative merging libraries. Slot caching is also incorporated to optimize performance. Users must manually install `tailwind-merge@^2` as a peer dependency. For projects using Tailwind CSS v4, it is explicitly recommended to use a corresponding v4 runtime variant solution.