Trailing slash options isn't enforced with splat route #5385

Which project does this relate to?

Router

Describe the bug

When you have a route defined with a splat such as some-testing.route.$.tsx and have a link like so:

<Link to="/some-testing/route/$" params={{ _splat: "" }} />

The generated path is always /some-testing/route/ regardless of trailingSlash option. If we try to instead of {{ _splat: undefined }} the route is /some-testing/route/undefined which is also incorrect.

Your Example Website or App

https://stackblitz.com/edit/github-oehqi8ag-yf2ynpjd?file=src%2Froutes%2F__root.tsx

Steps to Reproduce the Bug or Issue

1. Open stackblitz
2. Hover over Trailing Slash link and notice the href ends in slash

Expected behavior

Because the default trailingSlash option is set to never, it should always remove the trailing slash. Also, an undefined _splat should probably not render as undefined.

Screenshots or Videos

No response

Platform

• Router / Start Version: 1.132.33
• OS: macOS
• Browser: Chrome
• Browser Version: 140.0.7339
• Bundler: Vite
• Bundler Version: 7.1.17

Additional context

No response