Determine correct cache data lifecycle rules

[JesseTheRobot]

Tracking issue

[JesseTheRobot]

Current approach is as follows:

• Unpacked chunks shared an "ingress" cache, which is a two-tier (data_root and chunk) block-height based tagged LRU (data expires based on height the corresponding data root was last seen in a Tx, with some leeway for chunk gossip caching)
• PD chunks use a distinct single tier (chunks only) data cache, with logic that performs expiry based on the mempool state (if the corresponding consumer txs have been processed & no new consumer Txs have been added)