fix: surface errors from lazily loaded route modules instead of hanging the SSR stream

[birkskyum]

A syntax error in a route (or anything it imports) left the browser on a blank page with no error shown anywhere.

Every file route loads through lazy(). When the module fails to transform, its dynamic import rejects, and Solid's server-side lazy has no rejection path:

p = fn();
p.then(mod => p.resolved = mod.default);   // no .catch

So _loading stays true, the Suspense boundary never resolves, and renderToStream never closes. The document shell is flushed and the connection then hangs open forever, which is also why no Vite overlay appears: as far as the browser is concerned the page loaded fine.

withAssets already wraps the import on the server for asset collection, so this catches the rejection there and returns a module that throws during render. Solid routes that through catchError to the nearest ErrorBoundary, i.e. the dev overlay. Also covers a lazy chunk failing to load in production, which hung the stream the same way.

Errors in eagerly imported files (app.tsx, entry-server.tsx) were already handled and are unchanged.

Verified on apps/fixtures/basic with a broken component:

	before	after
load page while broken	request never completes, blank page	500, dev overlay shows the SyntaxError

Added lazy.spec.ts, which times out with "the SSR stream never closed" without the fix.

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🦋 Changeset detected

Latest commit: 380008c

The changes in this PR will be included in the next version bump.

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@solidjs/start	Patch

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commit: 380008c

[lxsmnsyc]

perhaps we can move this as an upstream issue?