Add .miners interaction to mock signing

[kantai]

Mock signing as implemented in #5020 has the signer set generate and broadcast signatures over stacks-node data. This will help test that signers are active, have up to date stacks nodes, and are configured correctly to broadcast p2p information.

However, testing that miners are also capable of receiving and broadcasting through .miners is also a useful test.

For this, 2.5 miners (via the neon_node module) should periodically read .signers looking for any mock signatures seen there. This vec of signatures (whether or not it is empty), should be combined with data like /v2/info, signed, and then broadcasted in .miners.

[blockstack-devops]

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