Return type of `sync_send_angles` is int, should not use method chaining.

[AkagawaTsurunaki]

Describe the bug
Return type of sync_send_angles is int, should not use method chaining.
See demo/sync.py at line 20-24.

To Reproduce
Steps to reproduce the behavior:

1. Clone the repository (Commit 3506655).
2. Run python .\demo\sync.py.
3. Input 3, Enter, Enter.

Expected behavior
The test case should be passed without any exceptions.

Screenshots

--------------------------------------------
| This file will test basic option method: |
|     sync_send_angles()                   |
--------------------------------------------


1 : COM4 - 蓝牙链接上的标准串行 (COM4)
2 : COM3 - 蓝牙链接上的标准串行 (COM3)
3 : COM5 - USB-Enhanced-SERIAL CH9102 (COM5)

Please input 1 - 3 to choice:3
COM5

Please input baud(default:115200):
115200

Wether DEBUG mode[Y/n]:

Start check basic options

Traceback (most recent call last):
  File "...\pymycobot\demo\sync.py", line 46, in <module>
    test(mycobot)
  File "...\pymycobot\demo\sync.py", line 20, in test
    mycobot.sync_send_angles([0, 0, 0, 0, 0, 0], 100).sync_send_angles(
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'int' object has no attribute 'sync_send_angles'

Desktop:

• OS: Windows 11
• Hardware: myCobot 280 M5 2023

Additional context
I fixed it by decomposing the method chaining:

    mycobot.sync_send_angles([0, 0, 0, 0, 0, 0], 100)
    mycobot.sync_send_angles([100, 50, 0, 0, 70, 160], 100)
    mycobot.sync_send_angles([-100,-50, 0, 0, -70,-160], 100)
    mycobot.set_free_mode(1)

I created a PR here but I do not know if it is a proper solution.

[anla-xu]

#145