feat: build tags y stubs para clickhouse y duckdb

Añade build tags noclickhouse/noduckdb a las implementaciones reales y
crea stubs que devuelven error para compilar sin las dependencias CGO.

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

functions/infra/clickhouse_open.go

@@ -1,3 +1,5 @@
+//go:build !noclickhouse
+
 package infra
 
 import (

functions/infra/clickhouse_open_stub.go

@@ -0,0 +1,13 @@
+//go:build noclickhouse
+
+package infra
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+// ClickHouseOpen is a stub when built with the noclickhouse tag.
+func ClickHouseOpen(host string, port int, user, password, database string) (*sql.DB, error) {
+	return nil, fmt.Errorf("clickhouse_open: clickhouse support not compiled (built with noclickhouse tag)")
+}

functions/infra/duckdb_open.go

@@ -1,3 +1,5 @@
+//go:build !noduckdb
+
 package infra
 
 import (

functions/infra/duckdb_open_stub.go

@@ -0,0 +1,13 @@
+//go:build noduckdb
+
+package infra
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+// DuckDBOpen is a stub when built with the noduckdb tag.
+func DuckDBOpen(path string) (*sql.DB, error) {
+	return nil, fmt.Errorf("duckdb_open: duckdb support not compiled (built with noduckdb tag)")
+}