feat(commands): blocking sorted-set operations (BZPOPMIN/BZPOPMAX/BZMPOP)

[TinDang97]

Summary

Moon has no blocking zset commands. Priority queues and scheduler patterns built on BZPOPMIN break.

Missing commands

• BZPOPMIN key [key ...] timeout
• BZPOPMAX key [key ...] timeout
• BZMPOP timeout numkeys key [key ...] MIN|MAX [COUNT count]

Design notes

• Shares the per-key wait-queue infrastructure from feat(commands): blocking list operations (BLPOP/BRPOP/BLMOVE/BLMPOP/BRPOPLPUSH) #56 (blocking list ops) — implement that first.
• Wake policy: on ZADD that inserts a new min/max, wake the oldest waiter whose side (MIN/MAX) matches. Score comparison determines whether the waiter gets the element or stays parked.
• Must preserve zset ordering invariants while waker fires (no lock-across-await).

Acceptance criteria

• Consistency tests for immediate, blocking, timeout, multi-key paths.
• Unblock on DEL/UNLINK/FLUSHDB.
• Dual-runtime support.

Depends on

• feat(commands): blocking list operations (BLPOP/BRPOP/BLMOVE/BLMPOP/BRPOPLPUSH) #56 (shared wait-queue primitive)

[pilotspacex-byte]

Closing — implemented in the same commit as #56: fff223b9 (PR #66, closing
#62). BZPOPMIN/BZPOPMAX/BZMPOP are wired through the same blocking registry
(src/blocking/, src/server/conn/blocking.rs) and metadata table.

Reopen if a specific edge case is found broken.

Author: Tin Dang tindang.ht97@gmail.com