Return `Result` from all `generate_*` methods #1734

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	6m 6s
build (1.65.0, wasm32-unknown-unknown)	3m 33s
build (stable, thumbv7em-none-eabi)	29s
build (stable, wasm32-unknown-unknown)	17s
minimal-versions	28s
test (1.65.0)	7m 47s
test (stable)	12s
	18m 52s

Provide feedback