Give each ModbusDeviceIdentification its own data

[kratos0718]

ModbusDeviceIdentification.stat_data is a class attribute and __init__, update() and __setitem__ all write into it, so every identity object shares one dict. The ModbusControlBlock keeps its own identity instance, so creating any identity anywhere also changes what a running server reports:

server_identity = ModbusDeviceIdentification(info_name={"VendorName": "Acme"})
ModbusControlBlock().Identity.update(server_identity)
ModbusDeviceIdentification(info_name={"VendorName": "SomethingElse"})
ModbusControlBlock().Identity.VendorName   # 'SomethingElse'

The fix copies the defaults into an instance dict in __init__. I added two tests to test/pdu/test_device.py, one for two independent identities and one for the control block case. Both fail on dev and pass with the change. test/pdu, test/server and test/simulator pass (1035 tests), and ruff and pylint are clean.

[janiversen]

LGTM, Thanks.

This is one that have been on my list for a long time, thanks for adding a solution.