Align README .quickdup filenames

[rogeralsing]

Summary

• update README to reflect strategy-specific .quickdup filenames
• note cache filename behavior in caching section
• add coverage for strategy-prefixed ignore file creation

Testing

• go test ./...

[rogeralsing]

Progress update:

• README now documents strategy-prefixed .quickdup filenames (results/cache/ignore).
• Added a test to lock in strategy-prefixed ignore file creation.
• Tests: go test ./...

[rogeralsing]

Progress: added unit tests to cover strategy-specific cache/ignore filenames and cache file writes. Ran go test ./... (ok).