MRG: standardize on u64 for scaled, and others #5843

Job	Run time
Check	34s
coverage	10m 3s
Lints (beta)	13s
Lints (stable)	13s
minimum_rust_version	7m 21s
Publish (dry-run)	5m 57s
test_all_features	13m 20s
test (beta)	1m 33s
Run tests under wasm32-wasi	1m 20s
test (stable)	1m 32s
Check if wasm-pack builds a valid package for the sourmash crate	1m 34s
test (windows)	2m 54s
test (macos)	1m 16s
Check if cbindgen runs cleanly for generating the C headers	8m 17s
	56m 7s

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