fix: reject eager_only with an already-narwhals LazyFrame#3677

gaoflow wants to merge 2 commits into

narwhals-dev:mainnarwhals-dev/narwhals:mainfrom

gaoflow:fix/3226-from-native-narwhals-lazy-eager-onlygaoflow/narwhals:fix/3226-from-native-narwhals-lazy-eager-onlyCopy head branch name to clipboard