chore: replace httpx with httpx2, register live mark in pytest.ini

pytest.ini

@@ -1,2 +1,4 @@
 [pytest]
 asyncio_mode = auto
+markers =
+    live: marks tests as live/integration tests (deselect with '-m "not live"')

requirements.txt

@@ -12,3 +12,5 @@ requests>=2.31
 
 # Testing
 pytest>=8.4
+pytest-asyncio>=1.0
+httpx2>=2.0