Fix Rust coldstart rustplus routing

[MarcStdt]

Summary

• expose rustplus in the Rust coldstart expectedPorts
• map rustplus to the generic coldstarter listener so TCP routing has ready idle endpoints

Test Plan

• env GOCACHE=/private/tmp/druid-go-cache make build-tree
• env GOCACHE=/private/tmp/druid-go-cache go test ./scripts/prebuild ./scripts/validate-release-workflow
• env GOCACHE=/private/tmp/druid-go-cache go run ./scripts/validate-scrolls.go
• env GOCACHE=/private/tmp/druid-go-cache ./scripts/validate_all_scrolls.sh

[druid-infra]

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