(new): support Bot API 10.3

(fix): finalize v2 contracts
(tests): cover v2 migration
(doc): prepare release guidance

migration_v2_test.go

@@ -0,0 +1,32 @@
+package laniakea
+
+import (
+	"context"
+	"testing"
+)
+
+func TestV2MigrationSurfaceCompiles(t *testing.T) {
+	runner := NewRunner[NoData]("sync", func(ctx context.Context, bot *Bot[NoData]) error {
+		return ctx.Err()
+	})
+	if runner.name != "sync" {
+		t.Fatalf("unexpected runner: %+v", runner)
+	}
+
+	if _, err := NewCallbackData("open", 42).Encode(BotPayloadCompact); err != nil {
+		t.Fatalf("Encode returned error: %v", err)
+	}
+
+	keyboard := NewInlineKeyboardJSON(2).AddCallbackButton("Open", "open", 42)
+	if _, err := keyboard.Get(); err != nil {
+		t.Fatalf("Get returned error: %v", err)
+	}
+
+	unlimited := NewInlineKeyboardJSON(1).
+		SetUnlimitedRows().
+		AddURLButton("A", "https://example.test/a").
+		AddURLButton("B", "https://example.test/b")
+	if _, err := unlimited.Get(); err != nil {
+		t.Fatalf("explicit unlimited keyboard failed: %v", err)
+	}
+}