Have another shot at vendoring pymodbus

We failed if pymodbus was already loaded, because Python doesn't load
anything already present in sys.modules.

Inspired by https://stackoverflow.com/a/76021423/1086121

custom_components/foxess_modbus/vendor/pymodbus/__init__.py

@@ -1,24 +1,46 @@
 import sys
 from pathlib import Path
+from contextlib import contextmanager
+from typing import Iterator
+
+
+@contextmanager
+def _load(path: Path, name: str) -> Iterator[None]:
+    def _remove_modules(name: str) -> None:
+        old_modules = {n: m for n, m in sys.modules.items(
+        ) if n == name or n.startswith(name + ".")}
+        for n in old_modules:
+            del sys.modules[n]
+        return old_modules
+
+    # Save and remove any existing loaded modules
+    old_modules = _remove_modules(name)
+
+    # Load the vendored module
+    sys.path.insert(0, str(path.absolute()))
+    yield ()
+    sys.path.pop(0)
+
+    # Remove anything we've added to the global modules
+    _remove_modules(name)
+    # Re-add any existing loaded modules
+    sys.modules.update(old_modules)
+
+
+with _load(Path(__file__).parent / "pymodbus-3.6.9", "pymodbus"):
+    from pymodbus.client import ModbusSerialClient
+    from pymodbus.client import ModbusTcpClient
+    from pymodbus.client import ModbusUdpClient
+    from pymodbus.exceptions import ConnectionException
+    from pymodbus.exceptions import ModbusIOException
+    from pymodbus.register_read_message import ReadHoldingRegistersResponse
+    from pymodbus.register_read_message import ReadInputRegistersResponse
+    from pymodbus.register_write_message import WriteMultipleRegistersResponse
+    from pymodbus.register_write_message import WriteSingleRegisterResponse
+    from pymodbus.pdu import ModbusResponse
+    from pymodbus.transaction import ModbusRtuFramer
+    from pymodbus.transaction import ModbusSocketFramer
 
-# Update python.analysis.extraPaths in .vscode/settings.json if you change this.
-# If changed, make sure subclasses in modbus_client are still valid!
-sys.path.insert(0, str((Path(__file__).parent / "pymodbus-3.6.9").absolute()))
-
-from pymodbus.client import ModbusSerialClient
-from pymodbus.client import ModbusTcpClient
-from pymodbus.client import ModbusUdpClient
-from pymodbus.exceptions import ConnectionException
-from pymodbus.exceptions import ModbusIOException
-from pymodbus.register_read_message import ReadHoldingRegistersResponse
-from pymodbus.register_read_message import ReadInputRegistersResponse
-from pymodbus.register_write_message import WriteMultipleRegistersResponse
-from pymodbus.register_write_message import WriteSingleRegisterResponse
-from pymodbus.pdu import ModbusResponse
-from pymodbus.transaction import ModbusRtuFramer
-from pymodbus.transaction import ModbusSocketFramer
-
-sys.path.pop(0)
 
 __all__ = [
     "ModbusSerialClient",