Return `Result` from all `generate_*` methods #1650

Job	Run time
minimal-versions	36s
build (1.65.0, thumbv7em-none-eabi)	5m 10s
clippy	5m 13s
build (1.65.0, wasm32-unknown-unknown)	6m 36s
build (stable, thumbv7em-none-eabi)	21s
test (1.65.0)	6m 17s
build (stable, wasm32-unknown-unknown)	12s
test (stable)	20s
	24m 45s

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