Added separate Solid 2 vitest config

[davedbase]

Adds configs/vitest.config.solid2.ts — a shared Vitest config using a direct Babel + babel-preset-solid@2.0.0-beta.12 transform instead of vite-plugin-solid, needed for packages whose tests use JSX with the Solid 2.0 @solidjs/web runtime (e.g. <For> children are now accessors)

• Adds @babel/core and babel-preset-solid@2.0.0-beta.12 to root devDependencies so configs/vitest.config.solid2.ts resolves the correct preset (root previously only had 1.x via vite-plugin-solid)
• Adds vitest2 / test:client2 / test:ssr2 scripts to root package.json, the package template, and packages/virtual — Solid 2.0 packages with JSX tests point test/test:ssr at vitest2; everything else keeps vitest

Why a separate config?

vite-plugin-solid bundles babel-preset-solid@1.x, which generates the _$effect(compute, apply) two-argument form incompatible with the Solid 2.0 runtime. The new config calls babel-preset-solid directly with moduleName: "@solidjs/web", producing correct output. Only packages with actual JSX in tests need this — the 20+ other already-migrated primitives use plain .ts tests and keep working with the existing config.

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