fix: Redis kvblock parsing bugs and add basic unit tests

[yankay]

Summary

This PR fixes 2 critical bugs in the Redis index implementation and adds unit tests for both Redis and in-memory kvblock index backends.

Changes Made

🐛 Bug Fixes

• ​​Fixed Redis pod identifier parsing​​: Modified the string split delimiter from : to @ to align with the expected PodEntry tostring format (podID@deviceTier). This change ensures accurate parsing when handling IPv6 addresses (which contain :) in PodEntry IP fields.
  But it's a break change when upgrading.
• Fixed Redis Lookup return value: Corrected slice boundary calculation from keys[:highestHitIdx] to keys[:highestHitIdx+1] to include the last hit key

✅ Testing Improvements

• Added basic unit tests for both Redis and in-memory index implementations
• Added miniredis dependency for lightweight Redis testing without external dependencies
  ref: Unit Tests #72

[vMaroon]

LGTM, thanks @yankay.