feat: add mock signature pubkey #1599

Job	Run time
test (cli, redis_tests)	15m 36s
distributions (ubuntu-latest, linux, x86_64-unknown-linux-gnu, x64, glibc)	10m 57s
test (sdk, stacks-signers)	8m 9s
distributions (windows-latest, windows, x86_64-pc-windows-msvc, x64)	19m 59s
distributions (macos-latest, darwin, x86_64-apple-darwin, x64)	7m 55s
distributions (macos-latest, darwin, aarch64-apple-darwin, arm64)	8m 30s
semantic-release	21s
build-publish (hirosystems/chainhook, chainhook-linux-x64-glibc, dockerfiles/components/chainhook...	9m 41s
auto-approve-dev	0s
deploy-dev	0s
deploy-staging	0s
auto-approve-stg	0s
deploy-prod	0s
	1h 21m 8s

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