Return `Result` from all `generate_*` methods #1315

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	3m 38s
build (1.65.0, thumbv7em-none-eabi)	3m 38s
build (1.65.0, wasm32-unknown-unknown)	3m 28s
build (1.65.0, wasm32-unknown-unknown)	3m 28s
build (stable, thumbv7em-none-eabi)	15s
build (stable, thumbv7em-none-eabi)	15s
build (stable, wasm32-unknown-unknown)	18s
build (stable, wasm32-unknown-unknown)	18s
test (1.65.0)	5m 4s
test (1.65.0)	3m 32s
test (stable)	25s
test (stable)	25s
minimal-versions / minimal-versions	32s
minimal-versions / minimal-versions	32s
	25m 48s

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