Fix #436 - Evict on 404 and notify listeners

[ltOgt]

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

• Adds bugfix for Cached file should be removed on 404, and error should be added to Stream even if a cached file exists #436
• Adds a test Outdated cacheFile should call to web, where 404 response should add Error to Stream and evict cache

⤵️ What is the current behavior?

• On an existing cacheFile and 404 on the update, listeners are not notified of the 404, and the file is not evicted.

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

• On 404 only, adds error to stream for existing cache file and evicts file

💥 Does this PR introduce a breaking change?

No

🐛 Recommendations for testing

Includes test

📝 Links to relevant issues/docs

#436

also see Baseflow/flutter_cached_network_image#898 for some related issues

🤔 Checklist before submitting

• All projects build
• Follows style guide lines (code style guide)
• ~~Relevant documentation was updated~~~
  • no documentation change needed
• Rebased onto current develop