feat: add Rslib Solid examples

[elecmonkey]

Summary

This PR adds three Rslib Solid examples:

• Solid v1 basic library example
• Solid v1 example integrated with Rstest
• Solid v2 beta basic library example

There is no Rstest example for Solid v2 because @solidjs/testing-library does not support Solid v2 yet.

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[elecmonkey]

Adding the Solid v2 beta example introduces solid-js@2.0.0-beta.x into the workspace. @tanstack/devtools declares a broad solid-js >=1.9.7 peer dependency, pnpm resolve the TanStack Devtools chain used by the React TanStack Start example against Solid v2. However it still import Solid v1-only entry points. As a result, the unrelated rsbuild/tanstack-start build fails after intruducing our solid v2 case...