fix: improve network response capture

[Vadman97]

Summary

Improve capture of HTTP response bodies for long-running requests.
Fix requestResponseSanitizer logic not working correctly with OTel code.

How did you test this change?

local SDK build with example app

testing sanitizer

Are there any deployment considerations?

---

Note

Medium Risk
Touches the browser OTel span lifecycle/export path and adds async coordination for response-body capture, which could affect span export timing and memory usage under load.

Overview
Fixes fetch span response-body capture by coordinating the async Response body clone/read with span export: applyCustomAttributesOnSpan stores a per-span promise in pendingResponseAttributes, and CustomBatchSpanProcessor.onEnd() awaits it (and now also flushes/cleans up on shutdown/forceFlush).

Adds applyRequestResponseSanitizer for the OTel path and runs it for both fetch and XHR spans (before and after response attributes are added), including honoring a null return by marking spans with highlight.record=false and skipping body capture to avoid leaks.

Expands the React Router e2e http-test page with new response-body capture and high-concurrency/memory-pressure test buttons, and reformats .vscode/JSON config files in the mobile .NET sample.

^{Written by Cursor Bugbot for commit 78541bc. This will update automatically on new commits. Configure here.}

[ccschmitz-launchdarkly]

Thank you for fixing this! One thought on the design of this and trying to avoid calling these internal methods, but I like the approach overall and think this is a great improvement!

[ccschmitz-launchdarkly]

Some relevant discussion around this functionality in the instrumentation-fetch repo: open-telemetry/opentelemetry-js#5293

Apparently they used to support this, but eliminated it because of potential memory pressure: open-telemetry/opentelemetry-js#5281

[Vadman97]

another round of testing - seems good. validated it's not causing memory pressure

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, have a team admin enable autofix in the Cursor dashboard.}