feat: Redis connection pool with worker affinity

[FumingPower3925]

Summary

Implement a connection pool for the Redis driver with the same worker-affinity model as the PostgreSQL driver. Redis connections are routed to the same engine worker as the HTTP connection.

Design

Package: driver/redis/pool.go

Pool Architecture

Same design as PostgreSQL pool:

type Pool struct {
    workers    []*workerPool   // one per engine worker
    standalone *standalonePool // fallback when no engine sharing
    overflow   *sharedPool     // shared pool for contention overflow
    pubsubPool *pubsubPool     // dedicated pool for Pub/Sub connections
}

Worker Affinity

Same flow as PostgreSQL:

1. HTTP request on worker N → pool.Get(ctx) checks workers[N] first
2. Fallback to overflow pool
3. Create new connection on worker N's event loop if needed
4. Release() returns to workers[N]

Redis-Specific Considerations

• AUTH + SELECT on connect: new connections authenticated and database selected before entering pool
• Pub/Sub connections: separate pool — Pub/Sub connections are in push mode and cannot be reused for commands
• MULTI/EXEC transactions: connection held exclusively during transaction (same as PG)
• Pipeline connections: can use pooled connections — pipeline commands are atomic from Redis's perspective

Configuration

type PoolConfig struct {
    MaxOpen      int           // max command connections (default: NumWorkers * 4)
    MaxIdle      int           // max idle per worker (default: 2)
    MaxLifetime  time.Duration // max connection lifetime (default: 30m)
    MaxIdleTime  time.Duration // max idle time (default: 5m)
    MaxPubSub    int           // max Pub/Sub connections (default: NumWorkers)
}

Modes

client, err := redis.NewClient("localhost:6379")                          // standalone
client, err := redis.NewClient("localhost:6379", redis.WithEngine(srv))   // integrated

Acceptance Criteria

• Per-worker pools with worker affinity
• Overflow to shared pool
• Separate Pub/Sub connection pool
• AUTH + SELECT on new connections
• Standalone mode with mini event loop
• Integrated mode sharing HTTP server's event loop
• Connection health check (PING)
• MaxOpen, MaxIdle, MaxLifetime, MaxIdleTime enforced
• Benchmark: pool Get/Release throughput

Dependencies

• Depends on 133 (Redis client — pool manages Redis connections)
• Depends on 113 (EventLoopProvider — for integrated mode)