iclouddrive: fix "cannot unmarshal number" error when listing photo albums

CloudKit is inconsistent about how it encodes the isDeleted field on
album records, returning a JSON boolean (true/false) for some accounts
and a number (0/1) for others. The numeric form caused listing of a
photo library to fail with:

    json: cannot unmarshal number into Go struct field
    ckBoolField.records.fields.isDeleted.value of type bool

The encoding also varies over time, not just per account: a full HTTP
dump from the reporting user showed the server sending

    "isDeleted" : { "value" : 0, "type" : "INT64" }

but the same account later reverted to the boolean encoding with no
client change. Asset records already deliver isDeleted as a number, so
both encodings are in active use server side and either may appear.

Accept both encodings when parsing CloudKit boolean fields.

See: https://forum.rclone.org/t/error-when-trying-to-list-contents-of-primarysync-directory-in-icloud-photos/54028

backend/iclouddrive/api/photos.go

@@ -1649,6 +1649,29 @@ type ckBoolField struct {
 	Value bool `json:"value"`
 }
 
+// UnmarshalJSON parses a CloudKit boolean field, accepting both the
+// boolean (true/false) and numeric (0/1) encodings the server uses
+func (b *ckBoolField) UnmarshalJSON(data []byte) error {
+	var raw struct {
+		Value json.RawMessage `json:"value"`
+	}
+	if err := json.Unmarshal(data, &raw); err != nil {
+		return err
+	}
+	if len(raw.Value) == 0 {
+		return nil
+	}
+	if err := json.Unmarshal(raw.Value, &b.Value); err == nil {
+		return nil
+	}
+	var n float64
+	if err := json.Unmarshal(raw.Value, &n); err != nil {
+		return fmt.Errorf("cannot unmarshal %q as CloudKit bool", raw.Value)
+	}
+	b.Value = n != 0
+	return nil
+}
+
 type ckReferenceField struct {
 	Value struct {
 		RecordName string `json:"recordName"`

backend/iclouddrive/api/photos_test.go

@@ -1283,3 +1283,34 @@ func TestAlbumCacheKey(t *testing.T) {
 		assert.True(t, (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f'), "key should be hex: %c", c)
 	}
 }
+
+func TestCkBoolFieldUnmarshal(t *testing.T) {
+	for _, test := range []struct {
+		in      string
+		want    bool
+		wantErr bool
+	}{
+		{`{"value": true}`, true, false},
+		{`{"value": false}`, false, false},
+		{`{"value": 1}`, true, false},
+		{`{"value": 0}`, false, false},
+		{`{"value": "INVALID"}`, false, true},
+	} {
+		var field ckBoolField
+		err := json.Unmarshal([]byte(test.in), &field)
+		if test.wantErr {
+			assert.Error(t, err, test.in)
+			continue
+		}
+		require.NoError(t, err, test.in)
+		assert.Equal(t, test.want, field.Value, test.in)
+	}
+
+	// isDeleted arrives as a number (0/1) on some accounts and as a
+	// boolean on others, so album records must parse both
+	var record albumRecord
+	err := json.Unmarshal([]byte(`{"recordName": "album1", "fields": {"isDeleted": {"value": 1}}}`), &record)
+	require.NoError(t, err)
+	require.NotNil(t, record.Fields.IsDeleted)
+	assert.True(t, record.Fields.IsDeleted.Value)
+}