refactor(dedup): redundant Snowflake override + shared Insert regex helper

Two follow-ups to the prior dedup pass:

- **Delete `Snowflake.UpdateBreakdown.GetSqlBreakdown`**: it was a
  byte-for-byte copy of the SqlServer base's `GetSqlBreakdown` (modulo
  one explanatory comment). Snowflake's UPDATE syntax — including the
  FROM clause — is identical at the formatter level, so the override
  was pure inheritance noise. Now inherits.

- **Extract `ParsePreparation.TryMatchInsertSql`**: the regex match +
  group extraction + failure message at the end of
  `SqlServer.InsertBreakdown.TryParse` and
  `Snowflake.InsertBreakdown.TryParse` was duplicated. Hoist the
  shared piece next to `TryRunPrelude` on `ParsePreparation`. Both
  callers continue to construct their own `InsertBreakdown` instance
  (the constructor signatures differ slightly between dialects).

All 1180 tests stay green.

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

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

@@ -44,35 +44,8 @@ public class UpdateBreakdown : SqlServerUpdateBreakdown
         WhereClause.Comment = whereComments.Count > 0 ? string.Join(" ", whereComments) : null;
     }
 
-    /// <summary>
-    /// Gets the SQL breakdown as a string for Snowflake.
-    /// </summary>
-    /// <returns>The UPDATE SQL statement.</returns>
-    protected override string GetSqlBreakdown()
-    {
-        var sb = new StringBuilder();
-
-        sb.AppendLine("UPDATE ");
-        sb.AppendLine($"     {TableName.Clause}");
-
-        sb.AppendLine("SET ");
-        sb.AppendLine($"     {SetClause.Clause}");
-
-        if (IsUsingFromClause)
-        {
-            // Snowflake supports FROM clause in UPDATE
-            sb.AppendLine("FROM ");
-            sb.AppendLine($"     {FromClause.Clause}");
-        }
-
-        if (IsUsingWhereClause)
-        {
-            sb.AppendLine("WHERE ");
-            sb.AppendLine($"     {WhereClause.Clause}");
-        }
-
-        return sb.ToString();
-    }
+    // GetSqlBreakdown() inherited from SqlServer.UpdateBreakdown — Snowflake's UPDATE syntax
+    // (including the optional FROM clause) is identical at the formatter level, so no override needed.
 
     #region Parse Methods