MRG: standardize on u32 for scaled, and introduce `ScaledType` #5911

Job	Run time
Check	37s
Check if cbindgen runs cleanly for generating the C headers	8m 28s
coverage	9m 53s
Lints (beta)	34s
Lints (stable)	34s
minimum_rust_version	7m 25s
Publish (dry-run)	5m 55s
test (beta)	1m 32s
Run tests under wasm32-wasi	1m 16s
test_all_features	13m 32s
test (stable)	1m 27s
Check if wasm-pack builds a valid package for the sourmash crate	1m 31s
test (windows)	3m 33s
test (macos)	1m 19s
	57m 36s

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