feat(storage): multi bucket download file api #3916

Job	Run time
test / test-dart-vm (3.3.0)	2m 10s
test / test-dart-vm (stable)	2m 10s
native_test / test-dart-native (macos-14)	3m 54s
ddc_test / test-dart-ddc (3.3.0, chrome)	3m 52s
native_test / test-dart-native (windows-latest)	4m 48s
dart2js_test / test-dart-2js (3.3.0, chrome)	4m 11s
ddc_test / test-dart-ddc (3.3.0, firefox)	4m 10s
dart2js_test / test-dart-2js (3.3.0, firefox)	4m 36s
ddc_test / test-dart-ddc (stable, chrome)	3m 33s
dart2js_test / test-dart-2js (stable, chrome)	4m 4s
ddc_test / test-dart-ddc (stable, firefox)	3m 43s
dart2js_test / test-dart-2js (stable, firefox)	4m 14s
	45m 25s

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