Fix clippy lints

[Rawk]

Fix a lot of Clippy lints. Mostly for files under programs/, but also enables unused_assignments for lib/.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 78 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
programs/zstdcli.rs	0.00%	59 Missing ⚠️
programs/dibio.rs	0.00%	6 Missing ⚠️
programs/fileio.rs	0.00%	5 Missing ⚠️
programs/util.rs	0.00%	5 Missing ⚠️
programs/datagen.rs	0.00%	3 Missing ⚠️

Flag	Coverage Δ
test-aarch64-apple-darwin	32.95% <0.00%> (+0.01%)	⬆️
test-aarch64-unknown-linux-gnu	31.61% <0.00%> (+<0.01%)	⬆️
test-i686-unknown-linux-gnu	31.67% <0.00%> (+<0.01%)	⬆️
test-x86_64-unknown-linux-gnu	32.98% <0.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
programs/fileio_asyncio.rs	0.00% <ø> (ø)
programs/main.rs	0.00% <ø> (ø)
programs/datagen.rs	0.00% <0.00%> (ø)
programs/fileio.rs	0.00% <0.00%> (ø)
programs/util.rs	0.00% <0.00%> (ø)
programs/dibio.rs	0.00% <0.00%> (ø)
programs/zstdcli.rs	0.00% <0.00%> (ø)

... and 4 files with indirect coverage changes

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[folkertdev]

Thanks for this!

We removed the rewrite to use &raw for now, because often that lint actually means that we should pass a reference instead, i.e. we need to look at it more carefully.