libs/common: Refactor libs/common 4 (#4237)

* libs/common: Refactor libs/common 4

- move byte function out of cmn to its own pkg
- move tempfile out of cmn to its own pkg
- move throttletimer to its own pkg

ref #4147

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* add changelog entry

* fix linting issues

libs/bytes/bytes.go

@@ -0,0 +1,62 @@
+package bytes
+
+import (
+	"encoding/hex"
+	"fmt"
+	"strings"
+)
+
+// The main purpose of HexBytes is to enable HEX-encoding for json/encoding.
+type HexBytes []byte
+
+// Marshal needed for protobuf compatibility
+func (bz HexBytes) Marshal() ([]byte, error) {
+	return bz, nil
+}
+
+// Unmarshal needed for protobuf compatibility
+func (bz *HexBytes) Unmarshal(data []byte) error {
+	*bz = data
+	return nil
+}
+
+// This is the point of Bytes.
+func (bz HexBytes) MarshalJSON() ([]byte, error) {
+	s := strings.ToUpper(hex.EncodeToString(bz))
+	jbz := make([]byte, len(s)+2)
+	jbz[0] = '"'
+	copy(jbz[1:], []byte(s))
+	jbz[len(jbz)-1] = '"'
+	return jbz, nil
+}
+
+// This is the point of Bytes.
+func (bz *HexBytes) UnmarshalJSON(data []byte) error {
+	if len(data) < 2 || data[0] != '"' || data[len(data)-1] != '"' {
+		return fmt.Errorf("invalid hex string: %s", data)
+	}
+	bz2, err := hex.DecodeString(string(data[1 : len(data)-1]))
+	if err != nil {
+		return err
+	}
+	*bz = bz2
+	return nil
+}
+
+// Allow it to fulfill various interfaces in light-client, etc...
+func (bz HexBytes) Bytes() []byte {
+	return bz
+}
+
+func (bz HexBytes) String() string {
+	return strings.ToUpper(hex.EncodeToString(bz))
+}
+
+func (bz HexBytes) Format(s fmt.State, verb rune) {
+	switch verb {
+	case 'p':
+		s.Write([]byte(fmt.Sprintf("%p", bz)))
+	default:
+		s.Write([]byte(fmt.Sprintf("%X", []byte(bz))))
+	}
+}