ref: Refactor some deprecated startSpan options

[mydea]

Mostly, changes origin to be set as an attribute, plus some further small adjustments.

In one case, we replaced headers data with a flattened headers.xxx object (astro).

In the case of bun, I also changed it to keep the request on the isolation scope (vs. the span).

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	77.16 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	68.38 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing, Replay with Canvas) - Webpack (gzipped)	72.32 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	61.93 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	32.65 KB (+0.01% 🔺)
@sentry/browser (incl. browserTracingIntegration) - Webpack (gzipped)	32.65 KB (+0.01% 🔺)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	31 KB (0%)
@sentry/browser (incl. sendFeedback) - Webpack (gzipped)	31.01 KB (0%)
@sentry/browser - Webpack (gzipped)	22.25 KB (0%)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	75.31 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	66.95 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	32.84 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	23.82 KB (0%)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	210.14 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	99 KB (-0.01% 🔽)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	71.02 KB (0%)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	35.93 KB (+0.02% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	68.67 KB (+0.01% 🔺)
@sentry/react - Webpack (gzipped)	22.28 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	85.1 KB (-0.01% 🔽)
@sentry/nextjs Client - Webpack (gzipped)	49.5 KB (-0.01% 🔽)
@sentry-internal/feedback - Webpack (gzipped)	17.1 KB (0%)