fix(blocklock,randomness): replace wonky block poller with custom stream

[azixus]

There seems to be an issue when using alloy's polling mechanism when fetching blocks on multiple agents sharing the same rpc provider:

{"timestamp":"2025-12-23T15:38:13.917317Z","level":"ERROR","fields":{"message":"failed to poll","err":"server returned an error response: error code -32000: filter not found"},"target":"alloy_rpc_client::poller"}
{"timestamp":"2025-12-23T15:38:13.917360Z","level":"WARN","fields":{"message":"server has dropped the filter, stopping poller"},"target":"alloy_rpc_client::poller"}

Per the log, it might be related to the use of the eth_*filter* RPC methods. This PR replaces it by using our own ticker + eth_blockNumber RPC call.

[AnomalRoil]

lgtm