feat(core): Adapt spans for client-side fetch to streaming responses

[chargome]

This PR makes spans for client-side fetch calls more accurate by cloning the response and adapting the span endTimestamp when the stream has been resolved.

fixes #12640

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser	22.43 KB (+0.15% 🔺)
@sentry/browser (incl. Tracing)	34.21 KB (+1.1% 🔺)
@sentry/browser (incl. Tracing, Replay)	70.25 KB (+0.48% 🔺)
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	63.58 KB (+0.53% 🔺)
@sentry/browser (incl. Tracing, Replay with Canvas)	74.65 KB (+0.46% 🔺)
@sentry/browser (incl. Tracing, Replay, Feedback)	87.22 KB (+0.4% 🔺)
@sentry/browser (incl. Tracing, Replay, Feedback, metrics)	89.07 KB (+0.34% 🔺)
@sentry/browser (incl. metrics)	26.74 KB (+0.1% 🔺)
@sentry/browser (incl. Feedback)	39.36 KB (+0.1% 🔺)
@sentry/browser (incl. sendFeedback)	27.05 KB (+0.14% 🔺)
@sentry/browser (incl. FeedbackAsync)	31.69 KB (+0.12% 🔺)
@sentry/react	25.21 KB (+0.14% 🔺)
@sentry/react (incl. Tracing)	37.21 KB (+0.86% 🔺)
@sentry/vue	26.58 KB (+0.13% 🔺)
@sentry/vue (incl. Tracing)	36.05 KB (+0.98% 🔺)
@sentry/svelte	22.57 KB (+0.16% 🔺)
CDN Bundle	23.61 KB (+0.09% 🔺)
CDN Bundle (incl. Tracing)	35.87 KB (+0.82% 🔺)
CDN Bundle (incl. Tracing, Replay)	70.25 KB (+0.44% 🔺)
CDN Bundle (incl. Tracing, Replay, Feedback)	75.52 KB (+0.41% 🔺)
CDN Bundle - uncompressed	69.33 KB (+0.01% 🔺)
CDN Bundle (incl. Tracing) - uncompressed	106.3 KB (+0.84% 🔺)
CDN Bundle (incl. Tracing, Replay) - uncompressed	217.94 KB (+0.41% 🔺)
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	230.76 KB (+0.39% 🔺)
@sentry/nextjs (client)	37.08 KB (+0.89% 🔺)
@sentry/sveltekit (client)	34.8 KB (+0.92% 🔺)
@sentry/node	111.9 KB (+0.01% 🔺)
@sentry/node - without tracing	89.33 KB (+0.01% 🔺)
@sentry/aws-serverless	98.49 KB (+0.01% 🔺)

[mydea]

sweet! great job on figuring out how to keep bundle size improvements outside of tracing to a minimum 🚀