Restore Sort unparser guard for correct ORDER BY placement

[krinart]

Restore the already_projected() guard in the Sort case of select_to_sql_recursively. Without it, queries with ORDER BY expressions generate invalid SQL when the Sort node follows an outer Projection.

Fixes:

• bench - tpcds - federated/postgres.yaml
• bench - clickbench - accelerated/s3[parquet]-sqlite[file].yaml
• clickbench - accelerated/spicecloud-duckdb[file].yaml

Upstream apache#20658

Problem

Two regressions in the DuckDB federation unparser after upgrading to DataFusion 52:

1. clickbench q25: Queries like SELECT "SearchPhrase" ... ORDER BY to_timestamp("EventTime") LIMIT 10 produce ORDER BY outside the subquery, referencing table names ("hits") that are out of scope.
2. tpcds q36: ORDER BY with GROUPING() expressions loses the derived_sort subquery alias, placing sort references outside their valid scope.

Root Cause

DF52's optimizer merges Limit into Sort as a fetch parameter, changing the plan shape from Projection → Limit → Sort → ... to Projection → Sort(fetch) → .... The Sort case previously had a guard that wrapped the sort into a derived_sort subquery when already_projected() was true. This guard was removed in DF52, causing ORDER BY and LIMIT to be placed on the outer query where inner table references are invalid.

Fix

Re-add the guard at the top of the Sort match arm in select_to_sql_recursively:

 if select.already_projected() {
     return self.derive_with_dialect_alias("derived_sort", plan, relation, false, vec![]);
 }