Improve SvelteKit client navigation spans #16549

Problem Statement

I noticed a while ago, that navigation spans are extremely short sometimes (1-5ms) which makes me a bit suspicious if we're not missing some spans (e.g. resource spans or similar).

Solution Brainstorm

• investigate with better e2e test routes
• perhaps stop directly ending the navigation span on the actual end of the navigation but rely on the idle span ending behaviour instead?
• ensure multiple quick subsequent navigations are still treated as separate traces and spans.