python-paho-mqtt: update to 2.1.0

Update package to 2.1.0. This is a major version bump with API changes
including new callback signatures.

Add PYPI_SOURCE_NAME since PyPI switched sdist filename to use
underscores (paho_mqtt-2.1.0.tar.gz).

Add PKG_BUILD_DEPENDS for python-hatchling since upstream switched
build backend from setuptools to hatchling.

Add test.sh to verify basic client functionality.

Signed-off-by: Alexandru Ardelean <alex@shruggie.ro>

lang/python/python-paho-mqtt/test.sh

@@ -0,0 +1,27 @@
+#!/bin/sh
+[ "$1" = python3-paho-mqtt ] || exit 0
+
+python3 - << 'EOF'
+import paho.mqtt.client as mqtt
+
+# Verify version
+assert hasattr(mqtt, '__version__') or hasattr(mqtt.Client, '__module__')
+
+# Test basic client instantiation
+client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2)
+assert client is not None
+
+# Test that the client has expected methods
+assert callable(getattr(client, 'connect', None))
+assert callable(getattr(client, 'publish', None))
+assert callable(getattr(client, 'subscribe', None))
+assert callable(getattr(client, 'disconnect', None))
+
+# Test MQTTMessage
+msg = mqtt.MQTTMessage(topic=b'test/topic')
+msg.payload = b'hello'
+assert msg.topic == 'test/topic'
+assert msg.payload == b'hello'
+
+print("paho-mqtt OK")
+EOF