fix(api): generate CallRaw + per-element decode for []<union> returns

GetChatAdministrators returns []ChatMember, where ChatMember is a
sealed-interface union. The codegen template emitted the generic
client.Call[..., []ChatMember] for it — encoding/json cannot unmarshal
a slice of an interface (no discriminator-aware path), so every real
response from Telegram failed at the parse step:

  telegram: parse: json: cannot unmarshal api.ChatMember into
  Go struct field Result[[]ChatMember].Result of type api.ChatMember

Fix is in cmd/genapi/methods.tmpl: add a third branch alongside the
existing single-union branch. When a method returns []<union>,
emit CallRaw + json.Unmarshal into []json.RawMessage + per-element
Unmarshal<Union>(e). Mirrors what GetChatMember (single-element)
already does, applied uniformly so any future slice-of-union method
Telegram introduces inherits the right shape.

Survey of v1.1.1 across all 23 sealed-interface unions confirms
GetChatAdministrators was the only broken site; the fix regenerates
just that one method body. New regression tests in
api/getchatadministrators_test.go cover the typical
admin+owner response and the empty-array case.

api/getchatadministrators_test.go

@@ -0,0 +1,55 @@
+package api
+
+import (
+	"context"
+	"testing"
+
+	"github.com/lukaszraczylo/go-telegram/client"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
+)
+
+// TestGetChatAdministrators_DecodesUnionSlice is a regression test for the
+// bug where GetChatAdministrators was emitted with the generic client.Call
+// against []ChatMember — encoding/json cannot unmarshal a slice of an
+// interface, so the call always failed at the parse step.
+//
+// The fix makes the codegen emit CallRaw + per-element UnmarshalChatMember
+// for any method returning []<sealed-interface union>.
+func TestGetChatAdministrators_DecodesUnionSlice(t *testing.T) {
+	body := `{"ok":true,"result":[
+		{"status":"creator","user":{"id":1,"is_bot":false,"first_name":"Owner"},"is_anonymous":false},
+		{"status":"administrator","user":{"id":2,"is_bot":false,"first_name":"Admin"},"can_be_edited":false,"is_anonymous":false,"can_manage_chat":true,"can_delete_messages":true,"can_manage_video_chats":false,"can_restrict_members":true,"can_promote_members":false,"can_change_info":true,"can_invite_users":true,"can_post_stories":false,"can_edit_stories":false,"can_delete_stories":false}
+	]}`
+
+	m := &mockDoer{}
+	m.On("Do", mock.Anything).Return(newJSONResp(200, body), nil)
+	bot := client.New("test:token", client.WithHTTPClient(m))
+
+	admins, err := GetChatAdministrators(context.Background(), bot,
+		&GetChatAdministratorsParams{ChatID: ChatIDFromInt(-100123)})
+	require.NoError(t, err)
+	require.Len(t, admins, 2)
+
+	owner, ok := admins[0].(*ChatMemberOwner)
+	require.True(t, ok, "first element must dispatch to ChatMemberOwner, got %T", admins[0])
+	require.Equal(t, int64(1), owner.User.ID)
+
+	admin, ok := admins[1].(*ChatMemberAdministrator)
+	require.True(t, ok, "second element must dispatch to ChatMemberAdministrator, got %T", admins[1])
+	require.True(t, admin.CanManageChat)
+	require.False(t, admin.CanPromoteMembers)
+}
+
+// TestGetChatAdministrators_EmptyArray covers the zero-admin edge case
+// (a basic group with no admins, or the bot itself filtered out).
+func TestGetChatAdministrators_EmptyArray(t *testing.T) {
+	m := &mockDoer{}
+	m.On("Do", mock.Anything).Return(newJSONResp(200, `{"ok":true,"result":[]}`), nil)
+	bot := client.New("test:token", client.WithHTTPClient(m))
+
+	admins, err := GetChatAdministrators(context.Background(), bot,
+		&GetChatAdministratorsParams{ChatID: ChatIDFromInt(-100123)})
+	require.NoError(t, err)
+	require.Empty(t, admins)
+}

api/methods.gen.go

@@ -2676,7 +2676,23 @@ type GetChatAdministratorsParams struct {
 //
 // Use this method to get a list of administrators in a chat. Returns an Array of ChatMember objects.
 func GetChatAdministrators(ctx context.Context, b *client.Bot, p *GetChatAdministratorsParams) ([]ChatMember, error) {
-	return client.Call[*GetChatAdministratorsParams, []ChatMember](ctx, b, "getChatAdministrators", p)
+	raw, err := client.CallRaw[*GetChatAdministratorsParams](ctx, b, "getChatAdministrators", p)
+	if err != nil {
+		return nil, err
+	}
+	var elems []json.RawMessage
+	if err := json.Unmarshal(raw, &elems); err != nil {
+		return nil, err
+	}
+	out := make([]ChatMember, 0, len(elems))
+	for _, e := range elems {
+		v, err := UnmarshalChatMember(e)
+		if err != nil {
+			return nil, err
+		}
+		out = append(out, v)
+	}
+	return out, nil
 }
 
 // GetChatMemberCountParams is the parameter set for GetChatMemberCount.