refactor(dedup): share clause-with-comments ingestion (PG/Snowflake QueryBreakdown ctors)

The `QueryBreakdown(string select, string from, ...)` constructors on
PostgreSql.QueryBreakdown and Snowflake.QueryBreakdown each ran the
same six-line pattern twice (once per clause): call
`parser.ExtractSqlComments`, set the clause to the trimmed result,
join the comment list into the Comment property.

New `StatementParser.PopulateClauseWithComments(rawText, target)`
instance method does both halves. Each ctor now reads:

    parser.PopulateClauseWithComments(selectClause, SelectClause);
    parser.PopulateClauseWithComments(fromClause, FromClause);

Same behavior; the helper is a pure refactor of existing semantics.

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

src/Strata.SqlTools.PostgreSql/Breakdowns/QueryBreakdown.cs

@@ -36,14 +36,8 @@ public class QueryBreakdown : SqlServerQueryBreakdown
     public QueryBreakdown(string selectClause, string fromClause, bool isMicrosoftSql = false) : base()
     {
         var parser = isMicrosoftSql ? Parser : PostgreSqlParserInstance;
-
-        var cleanSelect = parser.ExtractSqlComments(selectClause, out var selectComments);
-        SelectClause.Clause = cleanSelect.Trim();
-        SelectClause.Comment = selectComments.Count > 0 ? string.Join(" ", selectComments) : null;
-
-        var cleanFrom = parser.ExtractSqlComments(fromClause, out var fromComments);
-        FromClause.Clause = cleanFrom.Trim();
-        FromClause.Comment = fromComments.Count > 0 ? string.Join(" ", fromComments) : null;
+        parser.PopulateClauseWithComments(selectClause, SelectClause);
+        parser.PopulateClauseWithComments(fromClause, FromClause);
     }
 
     /// <summary>

src/Strata.SqlTools.Snowflake/Breakdowns/QueryBreakdown.cs

@@ -39,14 +39,8 @@ public class QueryBreakdown : SqlServerQueryBreakdown
     public QueryBreakdown(string selectClause, string fromClause, bool isMicrosoftSql = false) : base()
     {
         var parser = isMicrosoftSql ? Parser : SnowflakeParserInstance;
-
-        var cleanSelect = parser.ExtractSqlComments(selectClause, out var selectComments);
-        SelectClause.Clause = cleanSelect.Trim();
-        SelectClause.Comment = selectComments.Count > 0 ? string.Join(" ", selectComments) : null;
-
-        var cleanFrom = parser.ExtractSqlComments(fromClause, out var fromComments);
-        FromClause.Clause = cleanFrom.Trim();
-        FromClause.Comment = fromComments.Count > 0 ? string.Join(" ", fromComments) : null;
+        parser.PopulateClauseWithComments(selectClause, SelectClause);
+        parser.PopulateClauseWithComments(fromClause, FromClause);
     }
 
     /// <summary>

src/Strata.SqlTools.SqlServer/Statements/StatementParser.cs

@@ -140,6 +140,22 @@ public class StatementParser
     /// <param name="sql">The SQL statement containing comments.</param>
     /// <param name="comments">The extracted comments as a list of strings.</param>
     /// <returns>The SQL statement with comments removed.</returns>
+    /// <summary>
+    /// Runs <see cref="ExtractSqlComments"/> on <paramref name="rawText"/> and assigns the
+    /// cleaned text to <paramref name="target"/>'s <see cref="ISqlClause.Clause"/> (trimmed)
+    /// and the merged comments to its <see cref="ISqlClause.Comment"/>. Helper for
+    /// dialect-specific <c>QueryBreakdown</c> constructors that need to ingest
+    /// comment-bearing SQL fragments.
+    /// </summary>
+    /// <param name="rawText">The SQL fragment to clean.</param>
+    /// <param name="target">The clause to populate.</param>
+    public void PopulateClauseWithComments(string rawText, ISqlClause target)
+    {
+        var clean = ExtractSqlComments(rawText, out var comments);
+        target.Clause = clean.Trim();
+        target.Comment = comments.Count > 0 ? string.Join(" ", comments) : null;
+    }
+
 #pragma warning disable S3776 // Cognitive Complexity of methods should not be too high
 #pragma warning disable S127 // "for" loop stop conditions should be invariant
     public virtual string ExtractSqlComments(string sql, out List<string> comments)