Fix select_dtypes for quoted column identifiers (#242)

Fixes duckdb/duckdb#20329

`DuckDBPyRelation.select_dtypes` failed for relations with column names
that
require quoting (e.g., names containing spaces). The projection builder
did
not correctly quote identifiers, leading to binder errors.

This change ensures identifiers are quoted consistently and adds a
regression
test to cover the reported case.

Author: evertlammerts

src/duckdb_py/pyrelation.cpp

@@ -153,7 +153,7 @@ unique_ptr<DuckDBPyRelation> DuckDBPyRelation::ProjectFromTypes(const py::object
 			if (!projection.empty()) {
 				projection += ", ";
 			}
-			projection += names[i];
+			projection += KeywordHelper::WriteOptionallyQuoted(names[i]);
 		}
 	}
 	if (projection.empty()) {

tests/fast/test_relation.py

@@ -688,3 +688,10 @@ def create_view(con, view_name: str) -> None:
 
         res = con.sql("select * from vw").fetchall()
         assert res == expected
+
+    def test_relation_select_dtypes_quotes_identifiers_with_spaces(self, duckdb_cursor):
+        df = pd.DataFrame({"na me": ["alice", "bob"], "x": [1, 2]})
+        rel = duckdb_cursor.from_df(df)
+        out = rel.select_dtypes([duckdb.sqltypes.VARCHAR]).fetchdf()
+        assert list(out.columns) == ["na me"]
+        assert out["na me"].tolist() == ["alice", "bob"]