Add typing to examples.

[janiversen]

Add test example for write_registers, to ensure the different lists are legal.

[janiversen]

@MAKOMO I had to change the write_registers typing, to make it consistent with the internals, but to ensure it worked I added a test case in client_async_calls.py: async_write_registers_mypy just to check that mypy did not throw it out.

[MAKOMO]

@MAKOMO I had to change the write_registers typing, to make it consistent with the internals, but to ensure it worked I added a test case in client_async_calls.py: async_write_registers_mypy just to check that mypy did not throw it out.

Looks good to me! Thanks for those tests. They will be helpful in the future.

[janiversen]

If you want other typing tests, then please just add them to client_async_call.py, maybe rename write_registers_mypy to something like check_mypy.

The disadvantage for you is a bit work upfront, but the bigger advantage is that the typing is checked in every PR.