feat: add sendPaddlePurchase

[nikita-ushakov]

Summary

Adds sendPaddlePurchase as the Paddle counterpart to sendStripePurchase. After a checkout completes in Paddle.js, call this method with the transaction_id (and subscription_id for subscriptions) and the backend validates the purchase and grants entitlements before the promise resolves.

await Qonversion.shared.sendPaddlePurchase({
  price,
  currency,
  purchased,
  transactionId,
  customerId,
  productId,
  type,         // 'subscription' | 'inapp'
  subscriptionId, // required when type === 'subscription'; omit for 'inapp'
});

Wire flow

• QonversionInstance.sendPaddlePurchase
• → QonversionInternal.sendPaddlePurchase
• → PurchasesController.sendPaddlePurchase (logger + user id lookup, mirrors the stripe path)
• → PurchasesService.sendPaddlePurchase
• → RequestConfigurator.configurePaddlePurchaseRequest — POST /v3/users/{userId}/purchases with body:

  {
    "price": "...",
    "currency": "...",
    "purchased": ...,
    "paddle_store_data": {
      "transaction_id": "txn_...",
      "customer_id": "ctm_...",
      "product_id": "pro_...",
      "type": "subscription",
      "subscription_id": "sub_..."
    }
  }

  For one-time (type: 'inapp') purchases subscription_id is omitted from the body entirely.

Notes

• UserPurchase.stripeStoreData and UserPurchase.paddleStoreData are now both optional — a purchase row carries exactly one.
• PurchaseService grew a small private executePurchaseRequest helper to dedupe the success-or-throw shape between Stripe and Paddle.

Test plan

• yarn test → 220/220 (Jest)
• yarn tsc --noEmit clean
• New unit tests:
  • PurchasesService.test.ts: paddle success + paddle error
  • PurchasesController.test.ts: paddle success + paddle error
  • QonversionInternal.test.ts: sendPaddlePurchase delegation + log line
  • RequestConfigurator.test.ts: paddle subscription request body + paddle inapp request body (asserts subscription_id is omitted)