fix(rspress-plugin-mermaid): fix render id handling

[hangtiancheng]

Summary

• Serialize mermaid renders through a module-level queue because mermaid v10 render() is not reentrant: concurrent renders share temporary DOM elements keyed by the render id and corrupt each other's output
• Sanitize the React useId() value before using it as the mermaid render id; only : was stripped previously, while other React versions emit characters that must not leak into SVG ids and url(#...) marker references (e.g. «» in React 19.0-19.1)
• Skip redundant re-renders unless the diagram source or light/dark theme changed, and reset the cached state on render errors so retries work
• Resolve the component path from import.meta.dirname instead of __dirname so the plugin works in ESM
• Inline MermaidRendererProps in the component to keep the published component self-contained, and add rspress-plugin-mermaid as a devDependency for type checking
• Add docs coverage and Playwright e2e cases for concurrent rendering, dark-mode toggling, and invalid-diagram fallback

Test plan

• pnpm test passes
• pnpm exec rstest run --config rstest.e2e.config.ts packages/rspress-plugin-mermaid/index.spec.ts: 5 tests pass (SVG rendering, labels, concurrent diagrams, dark mode toggle, invalid diagram fallback)

[hangtiancheng]

The latest commit 19830f4 fixes the rs fmt --check failure.

The wrapped import in packages/rspress-plugin-mermaid/src/index.ts has been collapsed back to a single line.

[SoonIter]

Thanks ♥️～