Add RepairCache retention policies and cache CLI

[VKspyder2003]

Summary

This PR implements the cache retention and management features proposed in #59.

Changes

• Added configurable cache retention via:
  • max_age_days
  • max_entries
• Added automatic eviction after writes when retention limits are configured.
• Added public RepairCache.prune() API.
• Enhanced RepairCache.stats() to report configured retention settings.
• Added a new self-heal cache CLI command supporting:
  • --stats
  • --prune
  • --older-than
  • --max-age-days
  • --max-entries
• Added comprehensive unit and CLI tests covering:
  • validation
  • TTL pruning
  • size-based pruning
  • combined retention policies
  • automatic eviction
  • CLI behavior

Closes #59

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[ecc-tools]

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