feat: ingest `signer_signature` from `/new_block` event and expose in… #2574

Job	Run time
lint	58s
test (api)	10m 23s
test-2_5 (block-zero-handling)	1m 34s
test (bns)	3m 20s
test-2_5 (faucet-stx)	1m 15s
test (bns-e2e)	7m 5s
test-rosetta (rosetta)	3m 6s
test-2_5 (pox-4-btc-address-formats)	2m 12s
test (btc-faucet)	1m 28s
test-rosetta (rosetta-construction)	2m 17s
test-2_5 (pox-4-delegate-aggregation)	2m 16s
test (event-replay)	2m 3s
test-rosetta (rosetta-cli-data)	2m 13s
test-2_5 (pox-4-delegate-stacking)	1m 40s
test (rpc)	1m 31s
test-2_5 (pox-4-delegate-revoked-stacking)	1m 53s
test-rosetta (rosetta-cli-construction)	2m 25s
test-2_5 (pox-4-stack-extend-increase)	2m 21s
test-2_5 (pox-4-rosetta-btc-addr-types)	5m 1s
test-2_5 (pox-4-rosetta-cycle-phases)	1m 14s
test-2_5 (pox-4-rosetta-segwit)	1m 32s
test-2_5 (pox-4-burnchain-stack-stx)	1m 25s
test-2_5 (pox-4-burnchain-delegate-stx)	1m 43s
build-publish	1m 59s
	1h 2m 54s

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