Fix port conflicts for shared listeners

[anuruddhal]

Purpose

• Fix port conflicts for shared listeners
• https://github.com/wso2-enterprise/wso2-integration-internal/issues/2190
• [Bug]: bal build --cloud=k8s generates ports incorrectly ballerina-lang#44255

[Copilot]

Pull Request Overview

This PR addresses port conflicts for shared listeners by preventing duplicate service ports from being added to the service port list. The fix ensures that when multiple services share the same port, only one service port entry is created, avoiding conflicts in Kubernetes service definitions.

• Adds duplicate port checking logic to prevent port conflicts
• Implements early termination when a port is already defined in the service ports list

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