slot-based-collator: Refactor some internals #16572

Job	Run time
check-dependency-rules	11s
check-markdown	19s
check-workspace	22s
check-fail-ci	14s
check-readme	2m 57s
preflight / preflight	41s
preflight / ci-versions	1m 0s
fmt	1m 13s
check-rust-feature-propagation	2m 6s
check-toml-format	1m 5s
check-umbrella	2m 22s
test-rust-features	2m 0s
All quick checks passed	1s
	14m 31s

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