Implement selective tiering for lists (list tiering)

[romange]

Background

We want to implement selective tiering for list data structures . Lists may grow large and their oldest elements are often not actively accessed. Offloading old nodes to disk/storage enhances memory efficiency while retaining fast access to the newest elements.

Describe the solution you'd like

• Support offloading (tiering) of list nodes (quicklist nodes) once the list exceeds a configurable length K.
• When node_count > K, offload the first M nodes (where M ≤ K) to tiered storage.
• Each quicklist node contains a single listpack or a huge value, making it a good unit for offloading.

I/O Strategy

• Single-node operations (RPUSH, RPOP, LLEN, etc.):
  • No I/O required for operations on tail nodes (in-memory). Fast path for job queue usage.
• Multi-node operations (LRANGE, LINDEX, etc.):
  • Batch and parallelize reads for all required nodes to avoid sequential I/O round trips.

Open Questions

• Should K default to 1 (aggressive) or be dynamic based on memory pressure/self tuning?
• Should offload policy use a cooling or warmup period?
• When offloaded nodes are accessed, should they stay warm (in memory) or immediately become eligible for re-offloading?

Additional context

graph TB
    subgraph Queue ["List Structure"]
        N1["Node 1<br/>(oldest)<br/>TIERED"]
        N2["Node 2<br/>TIERED"]
        N3["..."]
        NM["Node M<br/>TIERED"]
        NM1["Node M+1<br/>IN-MEMORY"]
        NK["Node K<br/>(newest)<br/>IN-MEMORY"]
    end
    
    subgraph Disk ["Tiered Storage"]
        D1[Segment 1]
        D2[Segment 2]
        DM[Segment M]
    end
    
    N1 -.-> D1
    N2 -.-> D2
    NM -.-> DM
    
    style N1 fill:#e1f5ff,stroke:#0078d4
    style N2 fill:#e1f5ff,stroke:#0078d4
    style NM fill:#e1f5ff,stroke:#0078d4
    style NM1 fill:#d4f4dd,stroke:#107c10
    style NK fill:#d4f4dd,stroke:#107c10

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This feature is a sub-task of #6447 (selective tiering for hmap and lists).