test: verify network tracking end to end

[denrase]

📜 Description

• Add a real URLSession request test that verifies network breadcrumb URL, method, status code, and duration.
• Add a delayed local response and verify the resulting HTTP span includes the server delay.
• Include both end-to-end tests in the local test-server plan.
• Keep failed-request envelope snapshots isolated from unrelated network breadcrumbs.

💡 Motivation and Context

Verify that network breadcrumbs and HTTP performance span timing remain correct with potential Swift-backed networking changes in iOS 27.

Refs #8127

💚 How did you test it?

• swift test --package-path test-server
• Network breadcrumb end-to-end test on an iOS 27 simulator
• HTTP span timing end-to-end test on an iOS 27 simulator using test-without-building

📝 Checklist

• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.
• Public API changes reviewed by another Mobile SDK team member or implemented according to the develop docs spec.
• If I added a new public API, I also added it to the SentryObjC wrapper.

#skip-changelog