feat: abstracción DB multi-engine — CRUD genérico y openers para SQLite, Postgres, ClickHouse, DuckDB

Funciones Go con interfaz unificada para operaciones DB: open, close, create_table, exec, query, insert_row, insert_batch.
Openers específicos por engine. Tipo DBConfig para configuración común.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

functions/infra/db_exec.go

@@ -0,0 +1,22 @@
+package infra
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+// DBExec executes a non-SELECT statement (INSERT, UPDATE, DELETE, DDL) and
+// returns the number of rows affected. For statements that don't return rows
+// affected (e.g. DDL on some drivers), the count may be 0.
+func DBExec(db *sql.DB, query string, args ...any) (int64, error) {
+	result, err := db.Exec(query, args...)
+	if err != nil {
+		return 0, fmt.Errorf("db_exec: %w", err)
+	}
+	n, err := result.RowsAffected()
+	if err != nil {
+		// Some drivers don't support RowsAffected; treat as 0.
+		return 0, nil
+	}
+	return n, nil
+}