refactor: replaced Gift with Gift.Regular across APIs and data models

tgbotapi.core/src/commonMain/kotlin/dev/inmo/tgbotapi/types/gifts/Gifts.kt

@@ -7,5 +7,5 @@ import kotlinx.serialization.Serializable
 @Serializable
 data class Gifts(
     @SerialName(giftsField)
-    val gifts: List<Gift>
+    val gifts: List<Gift.Regular>
 )

tgbotapi.core/src/commonMain/kotlin/dev/inmo/tgbotapi/types/payments/stars/TransactionPartner.kt

@@ -60,7 +60,7 @@ sealed interface TransactionPartner {
         @SerialName(paidMediaPayloadField)
         val paidMediaPayload: PaidMediaPayload? = null,
         @SerialName(giftField)
-        val gift: Gift? = null
+        val gift: Gift.Regular? = null
     ) : TransactionPartner, SubscriptionPeriodInfo {
         @EncodeDefault
         override val type: String = Companion.type
@@ -75,7 +75,7 @@ sealed interface TransactionPartner {
         @SerialName(chatField)
         val chat: PreviewChat,
         @SerialName(giftField)
-        val gift: Gift? = null
+        val gift: Gift.Regular? = null
     ) : TransactionPartner {
         @EncodeDefault
         override val type: String = Companion.type
@@ -150,7 +150,7 @@ sealed interface TransactionPartner {
             val subscription_period: TimeSpan? = null,
             val paid_media: List<PaidMedia>? = null,
             val paid_media_payload: PaidMediaPayload? = null,
-            val gift: Gift? = null,
+            val gift: Gift.Regular? = null,
             val request_count: Int? = null,
             val sponsor_user: PreviewBot? = null,
             val commission_per_mille: Int? = null,