MRG: change `sig_from_record` to use scaled from `Record` to downsample #5968

Job	Run time
Lints (beta)	33s
coverage	10m 38s
Lints (stable)	37s
Check	33s
test (beta)	1m 32s
test_all_features	14m 15s
test (stable)	1m 31s
test (windows)	4m 8s
test (macos)	1m 36s
Check if cbindgen runs cleanly for generating the C headers	8m 43s
minimum_rust_version	7m 40s
Publish (on tags, dry-run otherwise)	11m 32s
Run tests under wasm32-wasi	1m 17s
Check if wasm-pack builds a valid package for the sourmash crate	1m 21s
	1h 5m 56s

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