test(bench): add allocation benchmarks for hot paths

Benchmark the pure translation functions on the per-message hot path:
entity conversion (both directions), reply-markup conversion, user
conversion and file_unique_id derivation, with -benchmem allocation
reporting.

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

Author: ernado

bench_test.go

@@ -0,0 +1,80 @@
+package botapi
+
+import (
+	"testing"
+
+	"github.com/gotd/td/fileid"
+	"github.com/gotd/td/tg"
+)
+
+// Benchmarks for the pure translation hot paths exercised on every incoming and
+// outgoing message. Run with: go test -bench . -benchmem
+
+func BenchmarkEntitiesToTg(b *testing.B) {
+	entities := []MessageEntity{
+		{Type: EntityBold, Offset: 0, Length: 4},
+		{Type: EntityItalic, Offset: 5, Length: 6},
+		{Type: EntityCode, Offset: 12, Length: 3},
+		{Type: EntityTextLink, Offset: 16, Length: 8, URL: "https://example.com"},
+		{Type: EntityTextMention, Offset: 25, Length: 5, User: &User{ID: 42}},
+	}
+	b.ReportAllocs()
+	for b.Loop() {
+		_ = entitiesToTg(entities)
+	}
+}
+
+func BenchmarkEntitiesFromTg(b *testing.B) {
+	entities := []tg.MessageEntityClass{
+		&tg.MessageEntityBold{Offset: 0, Length: 4},
+		&tg.MessageEntityItalic{Offset: 5, Length: 6},
+		&tg.MessageEntityCode{Offset: 12, Length: 3},
+		&tg.MessageEntityTextURL{Offset: 16, Length: 8, URL: "https://example.com"},
+		&tg.MessageEntityMentionName{Offset: 25, Length: 5, UserID: 42},
+	}
+	b.ReportAllocs()
+	for b.Loop() {
+		_ = entitiesFromTg(entities)
+	}
+}
+
+func BenchmarkReplyMarkupToTg(b *testing.B) {
+	q := "go"
+	markup := &InlineKeyboardMarkup{InlineKeyboard: [][]InlineKeyboardButton{
+		{
+			{Text: "site", URL: "https://example.com"},
+			{Text: "ok", CallbackData: "ok:1"},
+		},
+		{
+			{Text: "switch", SwitchInlineQuery: &q},
+		},
+	}}
+	b.ReportAllocs()
+	for b.Loop() {
+		if _, err := replyMarkupToTg(markup); err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+func BenchmarkUserFromTgUser(b *testing.B) {
+	u := &tg.User{
+		ID:        42,
+		FirstName: "Ada",
+		LastName:  "Lovelace",
+		Username:  "ada",
+		Bot:       false,
+	}
+	b.ReportAllocs()
+	for b.Loop() {
+		_ = userFromTgUser(u)
+	}
+}
+
+func BenchmarkFileUniqueID(b *testing.B) {
+	f := fileid.FileID{Type: fileid.Document, ID: 0x1122334455667788}
+	b.ReportAllocs()
+	for b.Loop() {
+		_ = fileUniqueID(f)
+	}
+}