Remove `std` feature; leverage `core::error::Error` #1801

Job	Run time
test (i686-unknown-linux-gnu, 1.81.0, sudo apt update && sudo apt install gcc-multilib)	1m 55s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	1m 47s
careful	1m 19s
build (1.81.0, thumbv7em-none-eabi)	45s
build-benchmarks	44s
test (x86_64-unknown-linux-gnu, 1.81.0)	1m 32s
build (1.81.0, wasm32-unknown-unknown)	40s
test (x86_64-unknown-linux-gnu, stable)	1m 30s
build (stable, thumbv7em-none-eabi)	38s
clippy	18s
build (stable, wasm32-unknown-unknown)	34s
cross (aarch64-unknown-linux-gnu, stable)	2m 51s
minimal-versions	22s
cross (powerpc-unknown-linux-gnu, stable)	2m 55s
doc	23s
miri (x86_64-unknown-linux-gnu)	3m 58s
miri (s390x-unknown-linux-gnu)	4m 10s
rustfmt	7s
	26m 28s

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