code-health: use hexadecimal codes for requests

Modern Tarantool documentation uses hexadecimal codes for request
codes [1].

1. https://www.tarantool.io/en/doc/latest/dev_guide/internals/box_protocol/

Part of #206

Author: DifferentialOrange

Diff for: tarantool/const.py

@@ -39,21 +39,21 @@
 IPROTO_GREETING_SIZE = 128
 IPROTO_BODY_MAX_LEN = 2147483648
 
-REQUEST_TYPE_OK = 0
-REQUEST_TYPE_SELECT = 1
-REQUEST_TYPE_INSERT = 2
-REQUEST_TYPE_REPLACE = 3
-REQUEST_TYPE_UPDATE = 4
-REQUEST_TYPE_DELETE = 5
-REQUEST_TYPE_CALL16 = 6
-REQUEST_TYPE_AUTHENTICATE = 7
-REQUEST_TYPE_EVAL = 8
-REQUEST_TYPE_UPSERT = 9
-REQUEST_TYPE_CALL = 10
-REQUEST_TYPE_EXECUTE = 11
-REQUEST_TYPE_PING = 64
-REQUEST_TYPE_JOIN = 65
-REQUEST_TYPE_SUBSCRIBE = 66
+REQUEST_TYPE_OK = 0x00
+REQUEST_TYPE_SELECT = 0x01
+REQUEST_TYPE_INSERT = 0x02
+REQUEST_TYPE_REPLACE = 0x03
+REQUEST_TYPE_UPDATE = 0x04
+REQUEST_TYPE_DELETE = 0x05
+REQUEST_TYPE_CALL16 = 0x06
+REQUEST_TYPE_AUTHENTICATE = 0x07
+REQUEST_TYPE_EVAL = 0x08
+REQUEST_TYPE_UPSERT = 0x09
+REQUEST_TYPE_CALL = 0x0a
+REQUEST_TYPE_EXECUTE = 0x0b
+REQUEST_TYPE_PING = 0x40
+REQUEST_TYPE_JOIN = 0x41
+REQUEST_TYPE_SUBSCRIBE = 0x42
 REQUEST_TYPE_ERROR = 1 << 15
 
 SPACE_SCHEMA = 272