Refactor: Use to_writer/from_reader across the codebase (#3443) #6152

Job	Run time
Check	34s
coverage	9m 53s
Lints (beta)	34s
Lints (stable)	34s
Publish (on tags, dry-run otherwise)	5m 42s
test (beta)	1m 36s
test_all_features	12m 37s
test (stable)	1m 23s
test (windows)	2m 51s
test (macos)	1m 14s
Run tests under wasm32-wasi	1m 10s
Check if wasm-pack builds a valid package for the sourmash crate	1m 28s
minimum_rust_version	6m 30s
Check if cbindgen runs cleanly for generating the C headers	8m 2s
	54m 8s

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