Refactor mock builder #19764

Job	Run time
check-code	13m 45s
Check for 'skip-ci' label	1s
check-msrv	5m 15s
lockbud	15m 29s
target-branch-check	1s
beacon-chain-tests	25m 22s
release-tests-ubuntu	35m 23s
release-tests-windows	46m 16s
basic-simulator-ubuntu	22m 10s
cargo-sort	13s
cargo-udeps	7m 29s
cli-check	15m 56s
compile-with-beta-compiler	15m 29s
debug-tests-ubuntu	5m 51s
ef-tests-ubuntu	12m 3s
execution-engine-integration-ubuntu	13m 55s
network-tests	27m 23s
fallback-simulator-ubuntu	19m 41s
op-pool-tests	24m 5s
slasher-tests	3m 44s
state-transition-vectors-ubuntu	8m 11s
test-suite-success	3s
	5h 17m 45s

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