Fix #436 - Evict on 404 and notify listeners

[ltOgt]

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

• Adds bugfix for #436
• Adds a test Outdated cacheFile should call to web, where 404 response should add Error to Stream and evict cache

:arrow_heading_down: 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.

:new: 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

:boom: Does this PR introduce a breaking change?

No

:bug: Recommendations for testing

Includes test

:memo: Links to relevant issues/docs

#436

also see https://github.com/Baseflow/flutter_cached_network_image/issues/898 for some related issues

:thinking: Checklist before submitting

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