Turbopack next/font: Use a custom enum instead of `Result` for failed local font files (#78941)
Previously, we used `anyhow::Result` for this, but this conflicts with
how we use `Error` in Turbo Tasks as system-level exceptions.
Test Plan: `pnpm test-dev-turbo
test/e2e/app-dir/next-font/next-font.test.ts`