refactor: fix clippy & unused imports/helper type #1118

Job	Run time
rust_stable	1m 14s
macos	3m 2s
minver	13s
macos-aarch64	1m 29s
rustfmt	14s
tier3 (x86_64-unknown-dragonfly)	59s
tier3 (x86_64-unknown-openbsd)	55s
tier3 (x86_64-unknown-haiku)	53s
linux_native_builds (x86_64-unknown-linux-gnu)	1m 59s
linux_native_builds (x86_64-unknown-linux-musl)	1m 57s
redox	37s
cross_compiling (aarch64-linux-android)	34s
cross (arm-unknown-linux-gnueabi)	1m 50s
cross_compiling (arm-linux-androideabi)	34s
cross (armv7-unknown-linux-gnueabihf)	1m 43s
cross_compiling (armv7-linux-androideabi)	32s
cross (i686-unknown-linux-gnu)	1m 41s
cross_compiling (i686-linux-android)	35s
cross_compiling (x86_64-linux-android)	36s
cross (i686-unknown-linux-musl)	1m 42s
cross_compiling (arm-unknown-linux-musleabi)	35s
cross (mips-unknown-linux-gnu)	1m 40s
cross_compiling (x86_64-unknown-fuchsia)	25s
cross (mips64-unknown-linux-gnuabi64)	1m 42s
cross_compiling (x86_64-unknown-illumos)	26s
cross (mips64el-unknown-linux-gnuabi64)	1m 52s
cross_compiling (aarch64-apple-ios, true)	27s
cross (mipsel-unknown-linux-gnu)	1m 39s
cross (powerpc64le-unknown-linux-gnu)	1m 39s
cross_compiling (powerpc64-unknown-linux-gnu)	34s
cross_compiling (s390x-unknown-linux-gnu)	37s
cross_compiling (x86_64-unknown-linux-gnux32)	35s
cross_compiling (x86_64-unknown-netbsd)	27s
	35m 57s

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