test(browser-integration-tests): Check trace envelope headers in trace lifetime tests

[Lms24]

This PR adds checks for the contents of the trace envelope headers in our new trace-lifetime test suite. The purpose of these checks is to ensure that we not only propagate and send correct trace data in request headers and Sentry events (trace context) but also in the trace envelope header.

Side note: This makes the tests notably longer but IMO its worth to have deep checks here because we can ensure that we always send the right data everywhere. Also, I had to write a "new" request parser to get both, events and the envelope headers.

ref #11599

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser	21.67 KB (added)
@sentry/browser (incl. Tracing)	31.46 KB (added)
@sentry/browser (incl. Tracing, Replay)	66.79 KB (added)
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	60.19 KB (added)
@sentry/browser (incl. Tracing, Replay with Canvas)	70.62 KB (added)
@sentry/browser (incl. Tracing, Replay, Feedback)	80.5 KB (added)
@sentry/browser (incl. Feedback)	35.25 KB (added)
@sentry/browser (incl. Feedback, Feedback Modal)	35.25 KB (added)
@sentry/browser (incl. Feedback, Feedback Modal, Feedback Screenshot)	37.28 KB (added)
@sentry/browser (incl. sendFeedback)	26.46 KB (added)
@sentry/react	24.35 KB (added)
@sentry/react (incl. Tracing)	34.37 KB (added)
@sentry/vue	25.2 KB (added)
@sentry/vue (incl. Tracing)	33.18 KB (added)
@sentry/svelte	21.79 KB (added)
CDN Bundle	24.03 KB (added)
CDN Bundle (incl. Tracing)	32.76 KB (added)
CDN Bundle (incl. Tracing, Replay)	66.4 KB (added)
CDN Bundle (incl. Tracing, Replay, Feedback)	82.6 KB (added)
CDN Bundle - uncompressed	70.86 KB (added)
CDN Bundle (incl. Tracing) - uncompressed	97.59 KB (added)
CDN Bundle (incl. Tracing, Replay) - uncompressed	207.25 KB (added)
@sentry/nextjs (client)	33.7 KB (added)
@sentry/sveltekit (client)	31.96 KB (added)
@sentry/node	155.86 KB (added)