Support for MSETEX

[mperice]

This ticket covers the implementation of the new Redis (introduced in 8.4) command MSETEX. This command atomically sets multiple string keys (numkeys) with a shared, single expiration time (TTL/PEXAT) in one operation. This guarantees consistency for both the key values and their expiries, which is essential for high-performance use cases in DragonflyDB.

Redis Documentation for MSETEX

MSETEX numkeys key value [key value ...] [NX | XX] [EX seconds | PX milliseconds | EXAT unix-time-seconds | PXAT unix-time-milliseconds | KEEPTTL]