test(document): add strict distributed search under churn

[Faolain]

Links:

• Flake investigation log + context: test(document): de-flake redundancy search test (ci:part2) #8
• Production fix for missing shard responses: fix(document): avoid premature partial search on missing RPC responses #9

What this adds:

• A targeted test that models a production client requiring a complete view under churn by using:
  • remote.throwOnMissing=true
  • increased remote.timeout
  • retries/backoff
• Important detail: the test uses on-disk block storage (per-peer temp directories) so that stop/start resembles a real restart (no data loss due to ephemeral in-memory blocks).

File:

• packages/programs/data/document/document/test/strict-search-under-churn.spec.ts

Local verification:

• PASS (10x): for i in {1..10}; do PEERBIT_TEST_SESSION=mock pnpm --filter @peerbit/document test -- --grep "strict search under churn" || break; done