elastic scaling: rework core selector handling #8784

Job	Run time
preflight / preflight	46s
preflight / ci-versions	55s
cargo-check-benches (master)	20m 46s
cargo-check-benches (current)	24m 22s
test-frame-ui	26m 48s
cargo-check-all-crate-macos	11m 28s
cargo-check-each-crate (1)	25m 42s
cargo-check-each-crate (2)	23m 27s
test-full-crypto-feature	2m 34s
cargo-check-each-crate (3)	6m 51s
test-node-metrics	12m 8s
cargo-check-each-crate (4)	24m 12s
cargo-check-each-crate (5)	32m 50s
cargo-check-each-crate (6)	13m 27s
cargo-check-each-crate (7)	30m 14s
test-frame-examples-compile-to-wasm	2m 55s
test-deterministic-wasm	7m 34s
check-tracing	2m 17s
check-metadata-hash	6m 49s
node-bench-regression-guard	12s
All test misc tests passed	1s
	4h 36m 18s

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