MRG: standardize on u64 for scaled, and others #5842

Job	Run time
Check	26s
Check if cbindgen runs cleanly for generating the C headers	3m 12s
coverage	9m 57s
Lints (beta)	12s
Lints (stable)	12s
minimum_rust_version	6m 58s
Publish (dry-run)	6m 17s
test (beta)	1m 31s
test (stable)	1m 33s
test (windows)	4m 18s
test (macos)	1m 50s
test_all_features	13m 25s
Run tests under wasm32-wasi	1m 19s
Check if wasm-pack builds a valid package for the sourmash crate	1m 26s
	52m 36s

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