chore(sonar): adopt Has.Count, Is.Empty, Does.Contain, char overloads in tests (NUnit2046, NUnit2011, CA1866)

- NUnit2046: `Assert.That(x.Count, Is.EqualTo(n))` → `Assert.That(x, Has.Count.EqualTo(n))` (or `Is.Empty` when n==0)
- NUnit2011: `Assert.That(s.Contains(x))` → `Assert.That(s, Does.Contain(x))` for richer failure messages
- CA1866: `.StartsWith("$"|"@"|":")` → `.StartsWith('$'|'@'|':')` char overload

Driven by `dotnet format analyzers --diagnostics NUnit2046 NUnit2011 CA1866`
for the cases the Roslyn fixer handles, plus a regex sweep for the remaining
`Count == n` (n>0) cases which the fixer doesn't address. CA1866 had no
associated code fix and was edited by hand (3 sites in 2 files). All tests
green (1180 passing).

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

tests/Strata.SqlTools.Snowflake.Tests/Snowflake/QueryBreakdownTests.cs

@@ -171,7 +171,7 @@ public class QueryBreakdownTests
         mainQueryBreakdown.AddWithClause("PRODUCT_ORDERS", cteSql);
 
         // Assert
-        Assert.That(mainQueryBreakdown.WithClauses.Count, Is.EqualTo(1));
+        Assert.That(mainQueryBreakdown.WithClauses, Has.Count.EqualTo(1));
         Assert.That(mainQueryBreakdown.WithClauses[0].TableName, Is.EqualTo("PRODUCT_ORDERS"));
     }
 
@@ -186,7 +186,7 @@ public class QueryBreakdownTests
         mainQueryBreakdown.AddWithClause("ProductOrders", cteSql, isMicrosoftSql: true);
 
         // Assert
-        Assert.That(mainQueryBreakdown.WithClauses.Count, Is.EqualTo(1));
+        Assert.That(mainQueryBreakdown.WithClauses, Has.Count.EqualTo(1));
         Assert.That(mainQueryBreakdown.WithClauses[0].TableName, Is.EqualTo("ProductOrders"));
     }
 
@@ -202,7 +202,7 @@ public class QueryBreakdownTests
         mainQueryBreakdown.AddWithClause("PRODUCT_ORDERS", cteQuery);
 
         // Assert
-        Assert.That(mainQueryBreakdown.WithClauses.Count, Is.EqualTo(1));
+        Assert.That(mainQueryBreakdown.WithClauses, Has.Count.EqualTo(1));
         Assert.That(mainQueryBreakdown.WithClauses[0].Query, Is.EqualTo(cteQuery));
     }
 
@@ -336,7 +336,7 @@ public class QueryBreakdownTests
 
         // Assert - Now using WITH clause
         Assert.That(query.IsUsingWithClause, Is.True);
-        Assert.That(query.WithClauses.Count, Is.EqualTo(1));
+        Assert.That(query.WithClauses, Has.Count.EqualTo(1));
     }
 
     #endregion
@@ -688,7 +688,7 @@ public class QueryBreakdownTests
         queryBreakdown.AddWithClause("ORDER_CTE", cte);
 
         // Assert
-        Assert.That(queryBreakdown.WithClauses.Count, Is.EqualTo(1));
+        Assert.That(queryBreakdown.WithClauses, Has.Count.EqualTo(1));
         Assert.That(queryBreakdown.IsUsingWithClause, Is.True);
     }
 
@@ -763,7 +763,7 @@ public class QueryBreakdownTests
         // Assert
         Assert.That(sql, Does.Contain("WITH"));
         Assert.That(sql, Does.Contain("MIDDLE_CTE AS ("));
-        Assert.That(mainQueryBreakdown.WithClauses.Count, Is.EqualTo(1));
+        Assert.That(mainQueryBreakdown.WithClauses, Has.Count.EqualTo(1));
     }
 
     [Test]
@@ -1511,7 +1511,7 @@ public class QueryBreakdownTests
         var snowflakeSql = result.GetSql();
 
         // Assert
-        Assert.That(result.WithClauses.Count, Is.EqualTo(1));
+        Assert.That(result.WithClauses, Has.Count.EqualTo(1));
         Assert.That(snowflakeSql, Does.Contain("WITH"));
         Assert.That(snowflakeSql, Does.Contain("ProductSummary AS ("));
     }