Subscription Model Modernisation

Problem Description

The billing team owns a Subscription value object that has been carrying the same shape since the codebase was ported from Java. The class lives at inputs/Subscription.kt. It holds the data fields a subscription needs — identifier, plan, status, billing period, renewal flag, timestamps — and has been carrying its own implementations of the standard object methods plus Java-bean style accessors since the port.

The team is modernising older value types to fit current project conventions. The Subscription class is the next in the queue. The change must preserve the field order and the externally-observable semantics — equality must still mean "same logical record," string representation must still surface every field, and callers constructing Subscription positionally must continue to compile.

Output Specification

Write the modernised file to output/Subscription.kt. Every field that the original class exposed must remain exposed; the field order must match the original; the public surface (construction, equality, toString) must be functionally equivalent.