avoid ordering and skew pitfalls when using pulsar's key_shared subscription

Steps

1. Choose Key_Shared when messages must be distributed across consumers but same-key or same-ordering-key messages must go to only one consumer.
2. Pick a mapping algorithm: Auto-split Hash Range or Auto-split Consistent Hashing for automatic load balancing, or the Sticky hash range policy for manual control.
3. If using the Sticky policy, manually assign hash ranges from 0 to 65535 per consumer and ensure the union of all ranges covers the full range, or messages in uncovered ranges get stuck.
4. To guarantee strict per-key ordering, use the sticky hash range policy and manage range splitting and coverage explicitly rather than relying on auto-split.
5. Monitor consumer scale-up and scale-down events, since auto-split hash ranges get reshuffled when consumers join or leave, temporarily affecting ordering guarantees.