chore(sonar): collapse trivial backing-field properties to auto-properties (S2292)

- WithClause.RecursiveQuery and WithClause.ColumnList had get/set bodies that
  only forwarded to private backing fields. Convert both to auto-properties
  and remove the now-orphaned _recursiveQuery / _columnList fields.

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

src/Strata.SqlTools.SqlBreakdown/Classes/WithClause.cs

@@ -29,8 +29,6 @@ public class WithClause : SqlClause, IWithClause
 {
     private SqlClauses? _sql;
     private IQueryBreakdown? _query;
-    private IQueryBreakdown? _recursiveQuery;
-    private List<string>? _columnList;
 
     /// <summary>
     /// Gets or sets the table name for the CTE.
@@ -115,11 +113,7 @@ public class WithClause : SqlClause, IWithClause
     /// Example recursive scenario: traversing an organizational hierarchy where employees reference their managers.
     /// </para>
     /// </remarks>
-    public IQueryBreakdown? RecursiveQuery
-    {
-        get => _recursiveQuery;
-        set => _recursiveQuery = value;
-    }
+    public IQueryBreakdown? RecursiveQuery { get; set; }
 
     /// <summary>
     /// Gets or sets the explicit column list for the CTE.
@@ -135,11 +129,7 @@ public class WithClause : SqlClause, IWithClause
     /// </list>
     /// The number of column names must match the number of columns in the SELECT clause.
     /// </remarks>
-    public List<string>? ColumnList
-    {
-        get => _columnList;
-        set => _columnList = value;
-    }
+    public List<string>? ColumnList { get; set; }
 
     /// <summary>
     /// Initializes a new instance of the <see cref="WithClause"/> class.