Implements RedisStore using github.com/redis/go-redis/v9 with Lua
scripts for atomic increment/decrement operations. Adds functional
options (WithRedisPassword, WithRedisDB, WithRedisPrefix), config
wiring via "redis" store_backend, and comprehensive tests covering
all 10 interface methods, concurrency, persistence, and error paths.
Co-Authored-By: Virgil <virgil@lethean.io>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
