Draft: verify recovery and reuse batch observations

[decofe]

Summary

• recover BatchSubmitted observations only from receipt-root- and logs-bloom-verified L1 receipts, not raw eth_getLogs
• bound the secure recovery fallback to eight concurrent header/receipt fetches
• fetch BatchFinalized logs once per monitor range and reuse them for the early-withdrawal decision and submission loop

Remaining work

• A durable subscriber-backed BatchSubmitted index is still needed to remove the historical recovery scan entirely. This draft establishes the verified observation path and removes the repeated steady-state query without adding a new persistence layer.

Verification

• cargo +nightly fmt --all --check
• cargo check -p tempo-zone-sequencer (blocked before compilation: pinned Commonware Git dependency returns HTTP 401)

Prompted by: @0xalpharush