Add empty `builder.buildApp` to workaround `@cloudflare/vite-plugin` build conflict

[hi-ogawa]

We can do this on our side, but let cloudflare folks know.

vite-plugin-react/packages/plugin-rsc/examples/starter-cf-single/vite.config.ts

Lines 53 to 57 in 6e4dfa7

	builder: {
	// empty buildApp to disable cloudflare's buildApp
	// https://github.com/cloudflare/workers-sdk/blob/19e2aab1d68594c7289d0aa16474544919fd5b9b/packages/vite-plugin-cloudflare/src/index.ts#L183-L186
	buildApp: async () => {},
	},