Use `coef: i128` in decimal (#1017) #451

Job	Run time
NIF 2.15 - aarch64-apple-darwin (macos-12 \| default)	37m 52s
NIF 2.15 - aarch64-unknown-linux-gnu (ubuntu-20.04 \| default)	22m 11s
NIF 2.15 - aarch64-unknown-linux-musl (ubuntu-20.04 \| default)	18m 32s
NIF 2.15 - x86_64-apple-darwin (macos-12 \| default)	35m 57s
NIF 2.15 - x86_64-pc-windows-gnu (windows-2022 \| default)	31m 55s
NIF 2.15 - x86_64-pc-windows-gnu (windows-2022 \| legacy_cpu)	30m 31s
NIF 2.15 - x86_64-pc-windows-msvc (windows-2019 \| default)	30m 36s
NIF 2.15 - x86_64-pc-windows-msvc (windows-2019 \| legacy_cpu)	29m 30s
NIF 2.15 - x86_64-unknown-freebsd (ubuntu-22.04 \| default)	19m 43s
NIF 2.15 - x86_64-unknown-freebsd (ubuntu-22.04 \| legacy_cpu)	19m 55s
NIF 2.15 - x86_64-unknown-linux-gnu (ubuntu-20.04 \| default)	17m 39s
NIF 2.15 - x86_64-unknown-linux-gnu (ubuntu-20.04 \| legacy_cpu)	17m 36s
NIF 2.15 - x86_64-unknown-linux-musl (ubuntu-20.04 \| default)	20m 23s
	5h 32m 20s

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