Add Tm Decoder

Update XM Decoder

algo/tm/xm.go

@@ -0,0 +1,47 @@
+package tm
+
+import (
+	"bytes"
+	"errors"
+	"github.com/umlock-music/cli/algo/common"
+)
+
+var magicHeader = []byte{0x00, 0x00, 0x00, 0x20, 0x66, 0x74, 0x79, 0x70}
+
+type Decoder struct {
+	file []byte
+}
+
+func (d *Decoder) GetCoverImage() []byte {
+	return nil
+}
+
+func (d *Decoder) GetAudioData() []byte {
+	return d.file[8:]
+}
+
+func (d *Decoder) GetAudioExt() string {
+	return ""
+}
+
+func (d *Decoder) GetMeta() common.Meta {
+	return nil
+}
+
+func NewDecoder(data []byte) *Decoder {
+	return &Decoder{file: data}
+}
+
+func (d *Decoder) Validate() error {
+	if len(d.file) < 8 {
+		return errors.New("invalid file size")
+	}
+	if !bytes.Equal(magicHeader, d.file[:8]) {
+		return errors.New("not a valid tm file")
+	}
+	return nil
+}
+
+func (d *Decoder) Decode() error {
+	return nil
+}