Fix validto computed property infinite calls problem

[murtaza-swati]

When subscription/v2-plan in DB has valid_to null, the /plan page make infinite calls to v_subscriptions and causing the page unresponsive.

The computed property is causing infinite calls because it depends on subscription.validTo, and within the computation, it makes a call to fetchV2Subscriptions.perform(), which likely modifies subscription.validTo. This causes the computed property to re-evaluate, leading to an infinite loop.

Fixed Approach with an Observer:
Ensure fetchV2Subscriptions doesn't modify subscription.validTo directly within the computed property, as this triggers recomputation.
Use computed properties for deriving state, and use observer to avoid side effect like fetching data.

[murtaza-swati]

closing in favour of #2942