Rewrite collator assignment to support parathreads #2308

Job	Run time
set-tags	6s
toml-formatting	59s
cargo-clippy	2m 18s
check-copyright	5s
cargo-toml-feature-propagation	2m 23s
typescript-formatting	20s
typescript-linting	20s
build	2m 42s
typescript-tests	0s
check-api-augment	0s
rust-test	0s
typescript-tests-flashbox	0s
typescript-dancebox-specs	0s
typescript-tests-frontier	0s
zombienet-tests	0s
typescript-tests-simple-template	0s
zombienet-tests-rotation	0s
chopsticks-upgrade-test	0s
zombienet-tests-warp-sync	0s
zombienet-test-upgrade	0s
docker-tanssi	0s
	9m 13s

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