Implement `INCREX` (Redis 8.8.0)

This is especially useful for rate limiters:

A common rate-limiting pattern requires atomically incrementing a counter and setting its expiration. With plain INCR and EXPIRE, this typically requires a Lua script to be atomic. INCREX requires a single native command.

Docs:

• https://redis.io/docs/latest/develop/whats-new/8-8/
• https://redis.io/docs/latest/commands/increx/