Refactor mock builder #19533

Job	Run time
lockbud	4m 16s
check-code	4m 33s
Check for 'skip-ci' label	1s
check-msrv	4m 25s
target-branch-check	1s
op-pool-tests	4m 36s
beacon-chain-tests	4m 17s
release-tests-windows	4m 1s
release-tests-ubuntu	4m 16s
ef-tests-ubuntu	4m 17s
basic-simulator-ubuntu	4m 25s
slasher-tests	3m 33s
network-tests	4m 25s
state-transition-vectors-ubuntu	4m 33s
cargo-udeps	4m 15s
cli-check	4m 26s
compile-with-beta-compiler	4m 13s
debug-tests-ubuntu	4m 16s
execution-engine-integration-ubuntu	4m 15s
fallback-simulator-ubuntu	4m 25s
cargo-sort	10s
test-suite-success	1s
	1h 17m 40s

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