Add iter_validators_by_ids

[evgeny-stakewise]

Summary

Adds iter_validators_by_ids in src/validators/consensus.py — an async generator that fetches beacon validators in chunks of settings.validators_fetch_chunk_size and yields flat ConsensusValidator instances. Callers no longer deal with batching or with the raw beacon dict.

async def iter_validators_by_ids(
    validator_ids: Sequence[str] | Sequence[HexStr],
    state_id: str = 'head',
    consensus_client: ExtendedAsyncBeacon | None = None,
) -> AsyncIterator[ConsensusValidator]

consensus_client defaults to the shared singleton, imported as default_consensus_client. It is overridable because node-status deliberately builds its own non-retry, 10s-timeout client to fail fast.

Changes

• src/validators/consensus.py — new iter_validators_by_ids; fetch_consensus_validators becomes a one-line async comprehension over it.
• src/exits/consensus.py — replaces manual range() slicing; int(beacon_validator['index']) and the raw pubkey lookup become validator.index / validator.public_key.
• src/commands/recover.py — replaces manual range() slicing; the pubkey/status normalization collapses to validator_statuses[validator.public_key] = validator.status.
• src/nodewise/status.py — _get_number_of_active_validators now iterates instead of issuing one unbatched request for every keystore public key, passing its own fail-fast client.

Normalization (0x-prefixing the pubkey, int() on the index, ValidatorStatus(...) on the status) now happens in one place: ConsensusValidator.from_consensus_data.

Behavior notes

• get_validator_public_keys in src/exits/consensus.py now returns 0x-prefixed public keys, consistent with the rest of the codebase.
• nodewise validator activity stats are now batched. Previously all keystore public keys went out in a single request, which could exceed request-size limits on a large keystore directory.

Tests

• New patch_consensus_client helper in src/common/tests/utils.py replaces 11 copies of the same patch('src.validators.consensus...') string across three test files.
• @contextmanager functions annotated -> Iterator[...] are deprecated in typeshed; switched to Generator[..., None, None] in the touched test files.