Adopt upstream RDB encoding for hash-field expiration

Dragonfly currently saves hashes with field expiration using the private RDB_TYPE_HASH_WITH_EXPIRY type (31),
with expiry stored as an RDB string in Dragonfly-relative seconds.

Add support for Redis 8 hash-expiry encodings and stop emitting the Dragonfly-specific format for new
snapshots. Prefer Redis types 24/25 because Dragonfly emits a REDIS header; Valkey type 22 should only be used with VALKEY080.

Scope:

• Load Redis RDB_TYPE_HASH_METADATA (24) and RDB_TYPE_HASH_LISTPACK_EX (25).
• Emit Redis encoding for new hash-expiry snapshots.
• Continue reading Dragonfly type 31 for backward compatibility.
• Handle the Redis minimum-expiry and per-field delta representation.
• Preserve persistent fields, expiry rounding, and overflow saturation.
• Avoid ambiguity with Redis’s pre-GA type 22 encoding.