Add a way to opt out of the default pending component

[LadyBluenotes]

Problem

Routes that render their own loading state have no way to opt out of the router's default pending component.

pendingComponent currently falls back to the configured default whenever a route is pending. Setting the option to null or undefined does not disable that fallback.

Proposed solution

Add an explicit opt-out value:

export const Route = createFileRoute('/example')({
  pendingComponent: 'never',
})

This should prevent the default pending component from rendering while preserving the route's pending behavior.

Opening this issue because there was PR #2658 addressing it but it is outdated now.