specialize `inflate_fast_help` for `avx2` #1230

Job	Run time
cargo-c dynamic library	11s
Clippy	28s
QEMU build & test (stable, ubuntu-latest, s390x-unknown-linux-gnu, s390x-linux-gnu-gcc)	56s
Clippy (--no-default-features --features="c-allocator")	23s
Build and test (stable, ubuntu-latest, x86_64-unknown-linux-gnu)	53s
QEMU build & test (stable, ubuntu-latest, i686-unknown-linux-gnu, i686-linux-gnu-gcc)	40s
Clippy (--no-default-features --features="rust-allocator")	23s
Build and test (msrv, ubuntu-latest, x86_64-unknown-linux-gnu)	1m 1s
Smoke-test fuzzing targets (default)	2m 35s
Smoke-test fuzzing targets (stable, macos-14, aarch64-apple-darwin)	2m 23s
Smoke-test fuzzing targets (c-allocator)	2m 36s
Build and test (beta, ubuntu-latest, x86_64-unknown-linux-gnu)	59s
Build and test (stable, macos-latest, x86_64-apple-darwin)	1m 9s
vanilla dynamic library	16s
Smoke-test fuzzing targets (rust-allocator)	2m 36s
Build and test (stable, macos-14, aarch64-apple-darwin)	1m 13s
Build and test (stable-x86_64-gnu, windows-2022, x86_64-pc-windows-gnu)	2m 22s
Miri	1m 44s
run flate2 test suite	21s
wasm32	52s
	24m 1s

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