Historical positions match the chain across eviction and restore

Soroban entries can expire and later be restored. A point-in-time read over one of those windows now answers the way the ledger says it happened.

• A position that was restored on-chain reads back with its full state for the ledgers it held it.
• A position that genuinely stopped existing is absent from historical reads.

No action needed: current state was unaffected; this corrects historical reads.