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.SqlBreakdown.Tests/ExpressionTests/BooleanExpressionTests.cs

@@ -24,8 +24,11 @@ public class BooleanExpressionTests : ExpressionTestsBase
 
         // Assert
         Assert.That(firstResult, Is.Not.SameAs(BooleanExpression.False));
-        Assert.That(firstResult, Is.AssignableTo<BooleanExpression>());
-        Assert.That(secondResult, Is.Not.SameAs(BooleanExpression.False));
+        Assert.Multiple(() =>
+        {
+            Assert.That(firstResult, Is.AssignableTo<BooleanExpression>());
+            Assert.That(secondResult, Is.Not.SameAs(BooleanExpression.False));
+        });
         Assert.That(secondResult, Is.TypeOf<AndExpression>());
     }