Add `bigdecimal` as a dependency #18

Job	Run time
cross-compile-linux	6s
install-macos-m1 (2.7)	50s
cross-compile-windows (x64-mingw32)	49s
install-windows-native (2.7)	3m 1s
install-macos-m1 (3.0)	25s
install-windows-native (3.0)	2m 2s
cross-compile-windows (x86-mingw32)	47s
install-macos-m1 (3.1)	28s
install-windows-native (3.1)	2m 19s
cross-compile-windows (x64-mingw-ucrt)	1m 1s
install-macos-m1 (3.2)	24s
install-windows-native (3.2)	2m 27s
install-macos-m1 (3.3)	26s
install-windows-native (3.3)	2m 53s
test-linux (2017, 2.7)	1m 21s
test-linux (2017, 3.0)	1m 16s
test-linux (2017, 3.1)	1m 12s
test-linux (2017, 3.2)	1m 9s
test-linux (2017, 3.3)	1m 17s
test-linux (2019, 2.7)	1m 43s
test-linux (2019, 3.0)	1m 17s
test-linux (2019, 3.1)	1m 27s
test-linux (2019, 3.2)	1m 29s
test-linux (2019, 3.3)	1m 13s
test-linux (2022, 2.7)	1m 23s
test-linux (2022, 3.0)	1m 13s
test-linux (2022, 3.1)	1m 13s
test-linux (2022, 3.2)	1m 11s
test-linux (2022, 3.3)	1m 10s
install-windows-mingw (2.7)	3m 50s
test-windows-mingw (2019, 2.7)	2m 53s
install-windows-mingw (3.0)	2m 15s
install-windows-ucrt (3.1)	1m 23s
test-windows-mingw (2019, 3.0)	2m 17s
test-windows-ucrt (2019, 3.1)	2m 10s
install-windows-ucrt (3.2)	1m 44s
test-windows-mingw (2022, 2.7)	3m 6s
test-windows-ucrt (2019, 3.2)	2m 4s
install-windows-ucrt (3.3)	2m 1s
test-windows-mingw (2022, 3.0)	1m 32s
test-windows-ucrt (2019, 3.3)	2m 36s
test-windows-ucrt (2022, 3.1)	2m 25s
test-windows-ucrt (2022, 3.2)	2m 28s
test-windows-ucrt (2022, 3.3)	3m 41s
	1h 13m 57s

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