Return `Result` from all `generate_*` methods #1310

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	5m 10s
test (1.65.0)	3m 32s
build (1.65.0, wasm32-unknown-unknown)	3m 34s
test (stable)	15s
build (stable, thumbv7em-none-eabi)	13s
build (stable, wasm32-unknown-unknown)	20s
minimal-versions / minimal-versions	25s
	13m 29s

Provide feedback