Bound oracle approval polling and handle registry root change gracefully

[cyc60]

Description

poll_validation_approval looped without an attempt cap: on persistent NotEnoughOracleApprovalsError (oracles split on the expected validator index, or stuck one short of threshold) it spun until an unrelated network deposit changed the registry root — minutes on mainnet, potentially hours on quiet networks — and while it spun, ValidatorTask processed no blocks (no event scanning, no withdrawal subtask). poll_consolidation_signature had the same unbounded loop, hanging the consolidate command on a threshold shortfall. Additionally, RegistryRootChangedError — routine control flow raised whenever the registry root moves mid-poll — was caught nowhere and landed in BaseTask's catch-all, logging an error and incrementing exception_count for expected behavior.

Both polling loops are now bounded by APPROVALS_MAX_ATTEMPTS (env-configurable, default 10): validation polling re-raises the last NotEnoughOracleApprovalsError, consolidation polling raises ConsolidationError. register_new_validators handles both expected outcomes — registry root changed (info log) and approvals not collected (warning) — by returning cleanly so the next task cycle retries with fresh state, keeping exception_count for genuine anomalies.