fix: remove unused image cache manager override

[usmanvrtx]

This PR removes the unused networkCacheManager override from the Image and Avatar controllers.

The override accepted only a runtime BaseCacheManager instance, which cannot be supplied through Ensemble YAML and has no in-repository caller. Image and Avatar continue to use Ensemble's internal cache manager, preserving redirect handling and configured cache behavior.

Related Issue

N/A

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)

What Has Changed

• Removed the unused networkCacheManager fields and setters from ImageController and AvatarController.
• Kept EnsembleImageCacheManager.instanceFor(allowRedirect: ...) as the manager used by Image and Avatar network requests.
• Renamed the framework Image helper parameter from networkCacheManager to cacheManager to clarify that it forwards the internally selected cache policy.
• Preserved allowRedirect: false redirect blocking and App.imageCache configuration for both Image and Avatar.

How to Test

1. Run the focused image widget tests:

   cd modules/ensemble
   flutter test test/widget/image_widget_test.dart

2. Verify an Image and Avatar with a network source still load normally.

3. Verify allowRedirect: false continues to reject redirected image requests.

4. Verify configured App.imageCache settings still apply to network images.

Screenshots / Videos

N/A

Checklist

• I have run flutter analyze and addressed any new warnings
• I have run flutter test and all tests pass
• I have tested my changes on the relevant platform(s)
• I have updated documentation if needed
• My changes do not introduce new warnings or errors

[TheNoumanDev]

Can you check main branch has this code, and in the main branch, the property name was networkCacheManager or cacheManager, and no flow is broken.

[usmanvrtx]

cacheManager name is internal use only and does not change any functionality or flow.

[TheNoumanDev]

Please verify the rest of your changes, any other stale changes please verify once again against each file, spend an hour on it, so that we dont have to come back again and fix things.