v1.6.7

• firehose-grpc-listen-addr and substreams-tier1-grpc-listen-addr flags now accepts comma-separated addresses (allows listening as plaintext and snakeoil-ssl at the same time or on specific ip addresses)
• removed old RegisterServiceExtension implementation (not used anywhere anymore)
• rpc-poller lib: fix fetching the first block on an endpoint (was not following the cursor, failing unnecessarily on non-archive nodes)