feat(nextjs): Skip OTEL root spans emitted by Next.js

[mydea]

We now skip any OTEL spans that Next.js emits, unless we already have a parent span that was created elsewhere (e.g. by our auto instrumentation). This way, we should be able to ensure consistent root spans for all cases.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser	21.67 KB (-2.23% 🔽)
@sentry/browser (incl. Tracing)	31.28 KB (-1.55% 🔽)
@sentry/browser (incl. Tracing, Replay)	66.59 KB (-0.73% 🔽)
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	59.99 KB (-0.84% 🔽)
@sentry/browser (incl. Tracing, Replay with Canvas)	70.43 KB (-0.67% 🔽)
@sentry/browser (incl. Tracing, Replay, Feedback)	80.28 KB (-0.64% 🔽)
@sentry/browser (incl. Feedback)	35.24 KB (-1.31% 🔽)
@sentry/browser (incl. Feedback, Feedback Modal)	35.25 KB (-1.31% 🔽)
@sentry/browser (incl. Feedback, Feedback Modal, Feedback Screenshot)	37.27 KB (-1.24% 🔽)
@sentry/browser (incl. sendFeedback)	26.46 KB (-1.81% 🔽)
@sentry/react	24.35 KB (-1.97% 🔽)
@sentry/react (incl. Tracing)	34.17 KB (-1.41% 🔽)
@sentry/vue	25.2 KB (-2.04% 🔽)
@sentry/vue (incl. Tracing)	32.99 KB (-1.45% 🔽)
@sentry/svelte	21.79 KB (-2.22% 🔽)
CDN Bundle	24.03 KB (-1.82% 🔽)
CDN Bundle (incl. Tracing)	32.58 KB (-1.26% 🔽)
CDN Bundle (incl. Tracing, Replay)	66.22 KB (-0.57% 🔽)
CDN Bundle (incl. Tracing, Replay, Feedback)	82.4 KB (-0.49% 🔽)
CDN Bundle - uncompressed	70.86 KB (-2.79% 🔽)
CDN Bundle (incl. Tracing) - uncompressed	96.98 KB (-2.06% 🔽)
CDN Bundle (incl. Tracing, Replay) - uncompressed	206.64 KB (-0.98% 🔽)
@sentry/nextjs (client)	33.51 KB (-1.51% 🔽)
@sentry/sveltekit (client)	31.77 KB (-1.53% 🔽)
@sentry/node	124.21 KB (-0.36% 🔽)