refactor and harden check_core_index #4967

Job	Run time
preflight / preflight	39s
preflight / ci-versions	55s
cargo-check-benches (master)	20m 49s
test-frame-ui	46m 8s
test-full-crypto-feature	2m 44s
cargo-check-benches (current)	24m 14s
cargo-check-each-crate (1)	25m 16s
test-node-metrics	12m 2s
cargo-check-each-crate (2)	21m 37s
cargo-check-each-crate (3)	8m 46s
cargo-check-each-crate (4)	21m 12s
cargo-check-each-crate (5)	30m 50s
cargo-check-all-crate-macos	12m 7s
cargo-check-each-crate (6)	14m 55s
cargo-check-each-crate (7)	31m 9s
test-frame-examples-compile-to-wasm	3m 11s
check-tracing	2m 31s
test-deterministic-wasm	7m 8s
node-bench-regression-guard	17s
check-metadata-hash	6m 57s
All test misc tests passed	1s
	4h 53m 28s

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