Refactor: Use to_writer/from_reader across the codebase #6147

Job	Run time
Check	23s
coverage	9m 26s
test (beta)	1m 32s
test (stable)	1m 24s
test_all_features	13m 4s
Check if wasm-pack builds a valid package for the sourmash crate	1m 22s
test (windows)	4m 11s
test (macos)	1m 49s
Check if cbindgen runs cleanly for generating the C headers	8m 2s
Lints (beta)	34s
Lints (stable)	23s
minimum_rust_version	6m 33s
Publish (on tags, dry-run otherwise)	5m 48s
Run tests under wasm32-wasi	1m 14s
	55m 45s

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