feat(proxyd): add Redis connection pool configuration options

[sluo10]

Summary

• Adds configurable Redis connection pool settings (pool size, idle connections, timeouts, retries) to RedisConfig
• Applies sensible defaults for high-throughput deployments (100 pool size, 20 min idle connections)
• Documents all new options in example.config.toml with explanations

Changes

• proxyd/config.go: Added 11 new pool configuration fields with documentation
• proxyd/redis.go: New NewRedisClientWithConfig() function that applies pool settings to both standard and cluster Redis clients
• proxyd/proxyd.go: Updated all Redis client instantiations to use the new config-aware constructor
• proxyd/example.config.toml: Added commented examples for all new configuration options