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.Rules.Tests/RuleEngineTests.cs

@@ -609,9 +609,12 @@ public class RuleEngineTests
         var result1 = await engine.RunRules(ruleSet1, input);
         var result2 = await engine.RunRules(ruleSet2, input);
 
-        // Assert
-        Assert.That(result1, Is.False, "First rule set should fail");
-        Assert.That(result2, Is.True, "Second rule set should pass");
+        Assert.Multiple(() =>
+        {
+            // Assert
+            Assert.That(result1, Is.False, "First rule set should fail");
+            Assert.That(result2, Is.True, "Second rule set should pass");
+        });
     }
 
     #endregion