test(providers): relocate provider-base scaffolding tests into unit leg

#287 added scaffolding/exceptions/strategy tests under tests/providers/base/,
but the providers CI leg only runs discovered provider subtrees (aws, k8s via
testconf.mk) and the unit leg runs tests/unit — so tests/providers/base ran in
NO CI leg. Move them into tests/unit/providers/base/ so the unit leg executes
them. Also replace the deprecated asyncio.get_event_loop().run_until_complete()
with asyncio.run() in the handler-base tests — get_event_loop() raises under
Python 3.12 once another test has closed the global loop, which surfaced as
order-dependent failures now that these run in the shared unit leg.

Author: fgogolli

tests/providers/base/scaffolding/__init__.py

@@ -120,7 +120,7 @@ def setup_method(self):
 
     def test_acquire_hosts_raises(self):
         with pytest.raises(NotImplementedError, match="acquire_hosts"):
-            asyncio.get_event_loop().run_until_complete(
+            asyncio.run(
                 self.handler.acquire_hosts(object(), object())
             )
 
@@ -130,7 +130,7 @@ def test_check_hosts_status_raises(self):
 
     def test_release_hosts_raises(self):
         with pytest.raises(NotImplementedError, match="release_hosts"):
-            asyncio.get_event_loop().run_until_complete(self.handler.release_hosts(["i-abc123"]))
+            asyncio.run(self.handler.release_hosts(["i-abc123"]))
 
     def test_cancel_resource_raises(self):
         with pytest.raises(NotImplementedError, match="cancel_resource"):
@@ -143,7 +143,7 @@ def test_get_example_templates_raises(self):
     def test_not_implemented_message_contains_classname(self):
         """Error message should name the class so developers know which handler to fix."""
         with pytest.raises(NotImplementedError) as exc_info:
-            asyncio.get_event_loop().run_until_complete(
+            asyncio.run(
                 self.handler.acquire_hosts(object(), object())
             )
         assert "_BareHandler" in str(exc_info.value)
@@ -178,7 +178,7 @@ def setup_method(self):
         self.handler = _ConcreteHandler()
 
     def test_acquire_hosts_returns_result(self):
-        result = asyncio.get_event_loop().run_until_complete(
+        result = asyncio.run(
             self.handler.acquire_hosts(object(), object())
         )
         assert result["resource_ids"] == ["r-1"]
@@ -188,18 +188,18 @@ def test_check_hosts_status_returns_result(self):
         assert "instances" in result
 
     def test_release_hosts_returns_none(self):
-        result = asyncio.get_event_loop().run_until_complete(self.handler.release_hosts(["i-1"]))
+        result = asyncio.run(self.handler.release_hosts(["i-1"]))
         assert result is None
 
     def test_release_hosts_accepts_context_dict(self):
         ctx = {"namespace": "default", "resource_mapping": {"i-1": ("fleet-1", 1)}}
-        result = asyncio.get_event_loop().run_until_complete(
+        result = asyncio.run(
             self.handler.release_hosts(["i-1"], context=ctx)
         )
         assert result is None
 
     def test_release_hosts_accepts_none_context(self):
-        result = asyncio.get_event_loop().run_until_complete(
+        result = asyncio.run(
             self.handler.release_hosts(["i-1"], context=None)
         )
         assert result is None