test: Improve Redis and Etcd test coverage

[abtreece]

Summary

• Refactored Redis client to use redisConn interface for mocking

• Added comprehensive Redis GetValues tests covering string, hash, and scan patterns

• Added Redis WatchPrefix and connectedClient tests

• Redis coverage improved from 6.9% to 51.0%

• Refactored Etcd client to use etcdKV interface for mocking

• Added comprehensive Etcd GetValues tests with mock transactions

• Etcd coverage improved from 12.1% to 37.9%

Overall project coverage improved from 40.2% to 44.9%

Test plan

• All existing tests pass
• New Redis tests pass with -vet=off (existing vet warnings in code)
• New Etcd tests pass
• Coverage verified with go test -coverprofile

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 39.85%. Comparing base (da3cdb4) to head (483eace).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/backends/etcd/client.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #320      +/-   ##
==========================================
+ Coverage   34.34%   39.85%   +5.50%     
==========================================
  Files          19       19              
  Lines        1706     1706              
==========================================
+ Hits          586      680      +94     
+ Misses       1061      955     -106     
- Partials       59       71      +12     

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