Allow retries after failed resized image downloads

[rahulshahDEV]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

Bug fix.

⤵️ What is the current behavior?

When a resized-image download fails, its completed broadcast stream remains in _runningResizes. A later request for the same image and dimensions reuses that stream and receives no response, so retrying does not load the image.

🆕 What is the new behavior (if this is a feature change)?

The in-flight resize entry is removed when its stream emits an error or completes. Errors still reach the caller, and an identity check prevents an old stream from removing a newer retry. A later request can download the image again.

💥 Does this PR introduce a breaking change?

No.

🐛 Recommendations for testing

• Flutter 3.47.4 stable: dart format --set-exit-if-changed ., flutter analyze, and flutter test --coverage passed (112 tests).
• The regression test first receives a 404, then retries the same resized URL and verifies that the successful response is returned.
• Example builds passed for Web, macOS, and iOS. The Android build could not download the Gradle wrapper distribution (Connection refused); Windows and Linux builds were not run locally. CI covers these targets.

📝 Links to relevant issues/docs

Fixes #439. Related symptom: Baseflow/flutter_cached_network_image#980.

🤔 Checklist before submitting

• All projects build
  • Local Web, macOS, and iOS builds passed. Android was blocked by the Gradle distribution download; Windows/Linux were not run locally. CI covers all targets.
• Follows style guide lines (code style guide)
• Relevant documentation was updated
• Rebased onto current main
• Version bumped and dated CHANGELOG entry added