feat: add GetStarTransactions

Returns the bot's Telegram Stars transaction history via
payments.getStarsTransactions (peer inputPeerSelf). The integer offset is
stringified into the MTProto pagination token, matching the official server.

Each tg.StarsTransaction maps to a Bot API StarTransaction: the sign of the raw
amount selects source (incoming) vs receiver (outgoing), and the raw
StarsTransactionPeer plus flags map onto the TransactionPartner sealed union
(User/Chat/Fragment/TelegramAds/TelegramApi/AffiliateProgram/Other), with
Fragment carrying a RevenueWithdrawalState union. These unions are outbound-only
and rely on plain encoding/json struct tags, matching ChatBoostSource.

Adds chatsByID/chatFromRaw helpers to build a Bot API Chat from raw
chat/channel peers offline.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: ernado

convert_member.go

@@ -1,6 +1,9 @@
 package botapi
 
-import "github.com/gotd/td/tg"
+import (
+	"github.com/gotd/td/constant"
+	"github.com/gotd/td/tg"
+)
 
 // chatMemberFromParticipant converts an MTProto channel participant into a Bot
 // API ChatMember. users maps user id to the resolved tg.User harvested from the
@@ -104,3 +107,75 @@ func usersByID(users []tg.UserClass) map[int64]*tg.User {
 
 	return m
 }
+
+// chatsByID indexes resolved tg.Chat/tg.Channel values from an MTProto response
+// by their raw (unmarked) id.
+func chatsByID(chats []tg.ChatClass) map[int64]tg.ChatClass {
+	m := make(map[int64]tg.ChatClass, len(chats))
+	for _, c := range chats {
+		switch c := c.(type) {
+		case *tg.Chat:
+			m[c.ID] = c
+		case *tg.ChatForbidden:
+			m[c.ID] = c
+		case *tg.Channel:
+			m[c.ID] = c
+		case *tg.ChannelForbidden:
+			m[c.ID] = c
+		}
+	}
+
+	return m
+}
+
+// chatFromRaw builds a Bot API Chat from a raw chat/channel peer, enriching it
+// from the resolved chats map when the peer is present. It works offline: when
+// the chat is absent only the marked id and kind are filled.
+func chatFromRaw(p tg.PeerClass, chats map[int64]tg.ChatClass) Chat {
+	var id constant.TDLibPeerID
+
+	switch p := p.(type) {
+	case *tg.PeerChat:
+		id.Chat(p.ChatID)
+
+		c := Chat{ID: int64(id), Type: ChatTypeGroup}
+
+		switch raw := chats[p.ChatID].(type) {
+		case *tg.Chat:
+			c.Title = raw.Title
+		case *tg.ChatForbidden:
+			c.Title = raw.Title
+		}
+
+		return c
+	case *tg.PeerChannel:
+		id.Channel(p.ChannelID)
+
+		c := Chat{ID: int64(id), Type: ChatTypeSupergroup}
+
+		switch raw := chats[p.ChannelID].(type) {
+		case *tg.Channel:
+			c.Title = raw.Title
+			c.Username = raw.Username
+			c.IsForum = raw.Forum
+			c.Type = channelChatType(raw.Broadcast)
+		case *tg.ChannelForbidden:
+			c.Title = raw.Title
+			c.Type = channelChatType(raw.Broadcast)
+		}
+
+		return c
+	default:
+		return Chat{}
+	}
+}
+
+// channelChatType reports the Bot API chat type for a channel by its broadcast
+// flag: broadcast channels are "channel", supergroups are "supergroup".
+func channelChatType(broadcast bool) ChatType {
+	if broadcast {
+		return ChatTypeChannel
+	}
+
+	return ChatTypeSupergroup
+}