fix: remove empty export from transpiled ts file

[John98Zakaria]

When doing an import, the typescript compiler automatically decides "well this file must be a module".

slidev/packages/client/setup/code-runners.ts

Lines 158 to 163 in f04f2eb

	const { transpile } = tsModule ??= await import('typescript')
	code = transpile(code, {
	module: tsModule.ModuleKind.ESNext,
	target: tsModule.ScriptTarget.ES2022,
	})
	return await context.run(code, 'javascript')

import type {UnionToIntersection} from 'type-fest' -> export {};

However, since the compiled TS code getts embedded in a function, the empty export code doesn't fit into the body of a function.

slidev/packages/client/setup/code-runners.ts

Lines 73 to 76 in f04f2eb

	try {
	const safeJS = `return async (console) => {${sanitizeJS(code)}}`
	// eslint-disable-next-line no-new-func
	await (new Function(safeJS)())(vmConsole)

Instead you get ERROR: SyntaxError: Unexpected token 'export'

See https://stackblitz.com/edit/github-qj6z8s?file=slides.md

This PR sanitizes the JS before running by removing the empty export {}; produced by typescript.

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