Fix cancelled HTTP requests showing as Pending in DevTools Network tab

[rishika0212]

Description

This PR fixes an issue where cancelled HTTP requests appear as "Pending" in the DevTools Network tab.

When a request is aborted (for example using HttpClientRequest.abort or Dio cancellation), DevTools keeps the request in a Pending state because no response is received. This change detects such cases and displays the request status as "Cancelled" instead.

Changes

• Detect cancelled/aborted requests in HttpRequestData
• Display "Cancelled" instead of "Pending" in the Network table
• Ensure cancelled requests are no longer treated as inProgress
• Prevent duration from remaining null for cancelled requests
• Add a regression test to verify the behavior
• Update CustomPointerScrollView to use cacheExtent so the project compiles with the current Flutter SDK

All existing network tests pass locally.

Fixes: #9593

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read the Flutter Style Guide recently and followed its advice.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I added tests to check the change I am making.

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[srawlins]

This code looks great; thanks for the PR! I'd like to test manually before landing.

[srawlins]

CC @elliette ; from the PR description:

Update CustomPointerScrollView to use cacheExtent so the project compiles with the current Flutter SDK

[bkonyi]

LGTM overall!

[bkonyi]

Ubernit: We can simply negate the entire expression rather than doing it twice

return !(_hasError
           ? _request.isRequestComplete
           : _request.isResponseComplete);