test: cast Assert.DoesNotThrow / Throws delegates to (Action) for NUnit 4

NUnit 4's Assert.DoesNotThrow / Assert.Throws<T> resolve delegate arguments
against multiple overloads (Action, TestDelegate, AsyncTestDelegate). A bare
() => lambda triggers CS0121 overload ambiguity once TrakHound#239 lands the NUnit 4
upgrade. The (Action) cast disambiguates unambiguously in both NUnit 3 and 4,
so the wrap is safe to land on this branch before TrakHound#239 merges.

Fixes cross-PR bug class discovered on integration/up-to-pr-249 build (158
errors, 112 CS0121 across 9 test files on 7 PRs). Per-PR fix — each affected
PR wraps its own new test sites so the class stays clean across the train.

Author: ottobolyos

tests/MTConnect.NET-Common-Tests/Agents/AgentUuidValidationTests.cs

@@ -601,15 +601,15 @@ public void Warn_delegate_emits_persisted_warn_only_when_override_null_and_persi
         [Test]
         public void Null_warn_delegate_does_not_throw_on_either_rejection_path()
         {
-            Assert.DoesNotThrow(() =>
+            Assert.DoesNotThrow((Action)(() =>
             {
                 _ = AgentUuidResolver.Resolve(
                     operatorSuppliedUuid: "not-a-uuid",
                     persistedUuid: "also-not-a-uuid",
                     agentName: "test-agent",
                     hostname: "test-host",
                     warn: null);
-            });
+            }));
         }
 
         /// <summary>
@@ -620,14 +620,14 @@ public void Null_warn_delegate_does_not_throw_on_either_rejection_path()
         [Test]
         public void Default_warn_argument_omitted_does_not_throw()
         {
-            Assert.DoesNotThrow(() =>
+            Assert.DoesNotThrow((Action)(() =>
             {
                 _ = AgentUuidResolver.Resolve(
                     operatorSuppliedUuid: "not-a-uuid",
                     persistedUuid: "also-not-a-uuid",
                     agentName: "test-agent",
                     hostname: "test-host");
-            });
+            }));
         }
 
         // ------------------------------------------------------------------
@@ -1056,7 +1056,7 @@ public void Resolve_warn_on_nil_uuid_uses_broad_acceptable_wording()
         public void Derive_throws_when_both_agent_name_and_hostname_are_empty(string agentName, string hostname)
         {
             Assert.Throws<ArgumentException>(
-                () => DeterministicAgentUuid.Derive(agentName, hostname, port: 0),
+                (Action)(() => DeterministicAgentUuid.Derive(agentName, hostname, port: 0)),
                 "Both seed components empty must not silently derive a fleet-wide collision UUID.");
         }