feat(eda): funciones de agregación/OLAP para AutomaticEDA (groupby/pivot push-down + selección LLM)

Cuatro funciones nuevas del grupo eda que nutren el capítulo AGREGACION:
- select_groupby_keys (pure): elige categóricas agrupables + numéricas medida desde el TableProfile.
- groupby_stats_duckdb (impure): GROUP BY push-down en DuckDB (count/mean/median/std/min/max por grupo).
- pivot_table_duckdb (impure): pivot A×B push-down, limitado a top filas/cols para no cortar.
- suggest_aggregations_llm (impure): el LLM elige las agregaciones interesantes con fallback determinista.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

python/functions/datascience/groupby_stats_duckdb_test.py

@@ -0,0 +1,106 @@
+"""Tests para groupby_stats_duckdb."""
+
+import os
+import sys
+
+import duckdb
+
+# Permitir importar funciones del registry (from infra import ..., from datascience import ...).
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", ".."))
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "functions"))
+
+from datascience.groupby_stats_duckdb import groupby_stats_duckdb
+
+
+def _make_db(tmp_path, rows):
+    """Crea una DuckDB con tabla t(g VARCHAR, x DOUBLE) e inserta `rows`."""
+    db = os.path.join(str(tmp_path), "t.duckdb")
+    con = duckdb.connect(db)
+    con.execute("CREATE TABLE t(g VARCHAR, x DOUBLE)")
+    con.executemany("INSERT INTO t VALUES (?, ?)", rows)
+    con.close()
+    return db
+
+
+def test_agrega_por_grupo_con_valores_conocidos(tmp_path):
+    # Grupo a: [10, 20, 30] -> n=3, mean=20, min=10, max=30, median=20, std=10.
+    # Grupo b: [5, 15]      -> n=2, mean=10, median=10.
+    # Grupo c: [100]        -> n=1, mean=100, std=None (1 sola fila).
+    rows = [
+        ("a", 10.0), ("a", 20.0), ("a", 30.0),
+        ("b", 5.0), ("b", 15.0),
+        ("c", 100.0),
+    ]
+    db = _make_db(tmp_path, rows)
+    res = groupby_stats_duckdb(db, "t", "g", ["x"])
+    assert res["status"] == "ok", res
+    assert res["n_groups"] == 3
+    assert res["truncated"] is False
+    assert res["aggs"] == ["count", "mean", "median", "std", "min", "max"]
+
+    by_key = {g["key"]: g for g in res["groups"]}
+    assert set(by_key) == {"a", "b", "c"}
+
+    # Grupo a: comprobacion manual de mean/min/max/median/std.
+    sa = by_key["a"]["stats"]["x"]
+    assert by_key["a"]["n"] == 3
+    assert abs(sa["mean"] - 20.0) < 1e-9
+    assert abs(sa["min"] - 10.0) < 1e-9
+    assert abs(sa["max"] - 30.0) < 1e-9
+    assert abs(sa["median"] - 20.0) < 1e-9
+    assert "std" in sa and sa["std"] is not None
+    assert abs(sa["std"] - 10.0) < 1e-9  # stddev_samp([10,20,30]) = 10
+
+    # Grupo b: mean y median conocidas.
+    sb = by_key["b"]["stats"]["x"]
+    assert by_key["b"]["n"] == 2
+    assert abs(sb["mean"] - 10.0) < 1e-9
+    assert abs(sb["median"] - 10.0) < 1e-9
+    assert "median" in sb and "std" in sb
+
+    # Grupo c: una sola fila -> std None (stddev_samp NULL), mean/min/max definidos.
+    sc = by_key["c"]["stats"]["x"]
+    assert by_key["c"]["n"] == 1
+    assert abs(sc["mean"] - 100.0) < 1e-9
+    assert sc["std"] is None
+
+
+def test_db_inexistente_devuelve_error_sin_lanzar(tmp_path):
+    db = os.path.join(str(tmp_path), "no_existe.duckdb")
+    res = groupby_stats_duckdb(db, "t", "g", ["x"])
+    assert res["status"] == "error", res
+    assert isinstance(res["error"], str) and res["error"]
+
+
+def test_measures_vacias_agrega_solo_count(tmp_path):
+    rows = [("a", 1.0), ("a", 2.0), ("b", 3.0)]
+    db = _make_db(tmp_path, rows)
+    res = groupby_stats_duckdb(db, "t", "g", [])
+    assert res["status"] == "ok", res
+    by_key = {g["key"]: g for g in res["groups"]}
+    assert by_key["a"]["n"] == 2
+    assert by_key["b"]["n"] == 1
+    # Sin measures, stats por grupo es un dict vacio (valido).
+    assert by_key["a"]["stats"] == {}
+    assert by_key["b"]["stats"] == {}
+
+
+def test_columna_con_espacio_agrupa_bien(tmp_path):
+    # Tabla con nombres de columna con espacios -> prueba el quoting con dobles
+    # comillas tanto en group_by como en la measure.
+    db = os.path.join(str(tmp_path), "space.duckdb")
+    con = duckdb.connect(db)
+    con.execute('CREATE TABLE t("my col" VARCHAR, "the val" DOUBLE)')
+    con.executemany(
+        'INSERT INTO t VALUES (?, ?)',
+        [("x", 1.0), ("x", 3.0), ("y", 10.0)],
+    )
+    con.close()
+
+    res = groupby_stats_duckdb(db, "t", "my col", ["the val"])
+    assert res["status"] == "ok", res
+    by_key = {g["key"]: g for g in res["groups"]}
+    assert by_key["x"]["n"] == 2
+    assert abs(by_key["x"]["stats"]["the val"]["mean"] - 2.0) < 1e-9
+    assert by_key["y"]["n"] == 1
+    assert abs(by_key["y"]["stats"]["the val"]["mean"] - 10.0) < 1e-9