feat: add shared extract-test-cache.sh script for HAF app test jobs

Consolidates cache extraction logic from balance_tracker and haf_block_explorer
into a shared script that all HAF apps can use.

Features:
- Exact cache key match only (no fallback to different app versions)
- Marker file prevents redundant extractions in same pipeline
- Optional PostgreSQL readiness wait with configurable timeout
- Handles pgdata permission fixing
- Proper error messages when cache not found

Also adds .fetch_extract_test_cache template for apps to fetch the script.

Apps can migrate from their local extract-cache-and-wait.sh scripts to use
this shared version for consistency and easier maintenance.