fix: resolve static route ID unions

[teemingc]

closes #

Stacked on #17024, which contains the regression test. Keeps static route-ID unions as a single resolve argument tuple while preserving correlated params for mixed unions.

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 4781c5b:

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Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/17025

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-17025-svelte.vercel.app/