[v8] Update span interface to new interface

[mydea]

We deprecated all the stuff on the span interface that will be removed in v8, now it's time to actually remove this!

### Tasks
- [ ] https://github.com/getsentry/sentry-javascript/pull/10687
- [x] Make sure we use `Span` interface everywhere in our APIs, not `SentrySpan`
- [ ] Remove all deprecated things on `Span` interface & make sure stuff still works with it
- [ ] https://github.com/getsentry/sentry-javascript/pull/10697
- [ ] https://github.com/getsentry/sentry-javascript/pull/10699
- [ ] https://github.com/getsentry/sentry-javascript/pull/10698