Fix cancelled HTTP requests showing as Pending in DevTools Network tab (#9685)

## 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

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