chore(sonar): wrap independent assertions in Assert.Multiple (NUnit2045)

Driven by `dotnet format analyzers --diagnostics NUnit2045`. The fixer
groups consecutive independent `Assert.That(...)` calls into
`Assert.Multiple(() => { ... })`, so a failing assertion no longer
short-circuits the block — every failure inside the group is reported,
which gives much better diagnostics on multi-property tests.

Audit confirmed no Assert.Throws / Assert.Fail / Assert.Catch / Assert.Pass
/ Assert.DoesNotThrow got pulled inside a Multiple block (those need to
short-circuit). All 1180 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Strata.SqlTools.LinqToSql.Tests/QueryValidatorTests.cs

@@ -62,9 +62,12 @@ public class QueryValidatorTests
         validator.Validate(breakdown2);
         var count2 = validator.Issues.Count;
 
-        // Assert
-        Assert.That(count1, Is.GreaterThan(0));
-        Assert.That(count2, Is.GreaterThan(0));
+        Assert.Multiple(() =>
+        {
+            // Assert
+            Assert.That(count1, Is.GreaterThan(0));
+            Assert.That(count2, Is.GreaterThan(0));
+        });
     }
 
     #endregion
@@ -324,10 +327,13 @@ public class QueryValidatorTests
         var infos = validator.GetIssuesBySeverity(ValidationSeverity.Info);
         var errors = validator.GetIssuesBySeverity(ValidationSeverity.Error);
 
-        // Assert
-        Assert.That(warnings, Is.Not.Empty);
-        Assert.That(infos, Is.Not.Empty);
-        Assert.That(errors, Is.Empty);
+        Assert.Multiple(() =>
+        {
+            // Assert
+            Assert.That(warnings, Is.Not.Empty);
+            Assert.That(infos, Is.Not.Empty);
+            Assert.That(errors, Is.Empty);
+        });
     }
 
     #endregion
@@ -349,8 +355,11 @@ public class QueryValidatorTests
 
         // Assert
         Assert.That(validator.Issues, Has.Count.EqualTo(1));
-        Assert.That(validator.Issues[0].Code, Is.EqualTo("CUSTOM_001"));
-        Assert.That(validator.HasErrors, Is.True);
+        Assert.Multiple(() =>
+        {
+            Assert.That(validator.Issues[0].Code, Is.EqualTo("CUSTOM_001"));
+            Assert.That(validator.HasErrors, Is.True);
+        });
     }
 
     [Test]
@@ -365,9 +374,12 @@ public class QueryValidatorTests
             .AddIssue(ValidationSeverity.Warning, "WARN_001", "Warning 1")
             .AddIssue(ValidationSeverity.Info, "INFO_001", "Info 1");
 
-        // Assert
-        Assert.That(result, Is.SameAs(validator));
-        Assert.That(validator.Issues, Has.Count.EqualTo(3));
+        Assert.Multiple(() =>
+        {
+            // Assert
+            Assert.That(result, Is.SameAs(validator));
+            Assert.That(validator.Issues, Has.Count.EqualTo(3));
+        });
     }
 
     #endregion
@@ -480,9 +492,12 @@ public class QueryValidatorTests
         // Act
         var validator = QueryValidator.ValidateQuery(breakdown);
 
-        // Assert
-        Assert.That(validator.Issues.Count, Is.GreaterThan(1));
-        Assert.That(validator.HasWarnings, Is.True);
+        Assert.Multiple(() =>
+        {
+            // Assert
+            Assert.That(validator.Issues.Count, Is.GreaterThan(1));
+            Assert.That(validator.HasWarnings, Is.True);
+        });
     }
 
     [Test]