Enable `-Wconversion` #360

Job	Run time
coding-style	8s
host-win-msvc	59s
host-arm (armv7, none, none, g++)	3m 13s
host-win (x86_64)	49s
host-arm (armv7, none, none, clang++-15)	1m 37s
host-x86 (x86_64, g++)	1m 57s
host-win (armv7)	1m 10s
host-arm (aarch64, none, none, g++)	2m 45s
host-x86 (x86_64, clang++)	4m 6s
host-win (aarch64)	43s
host-arm (aarch64, none, none, clang++-15)	1m 43s
host-arm (aarch64, crypto+crc, none, g++)	2m 45s
host-arm (aarch64, crypto+crc, none, clang++-15)	1m 43s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, g++)	3m 20s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, clang++-15)	1m 42s
test-win-msvc	54s
	29m 34s

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