Subscription hub

[Yunusabdul38]

This implementation adds support for multi-location (hub) subscriptions to the Soroban smart contract. Users can now have subscriptions tied to specific hubs/locations, enabling organizations to manage memberships across multiple physical or virtual locations.

Updated Subscription Struct (types.rs)

pub struct Subscription {
    pub id: String,
    pub hub_id: String,  // NEW: Hub identifier
    pub user: Address,
    pub payment_token: Address,
    pub amount: i128,
    pub status: MembershipStatus,
    pub created_at: u64,
    pub expires_at: u64,
}

closes: #222

[vercel]

@Yunusabdul38 is attempting to deploy a commit to the naijabuz's projects Team on Vercel.

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