Added union method to HLL #5521

Job	Run time
Check	37s
coverage	10m 20s
Lints (beta)	43s
test (beta)	1m 56s
Lints (stable)	50s
test (stable)	1m 58s
test_all_features	13m 57s
Run tests under wasm32-wasi	2m 4s
test (windows)	3m 36s
Check if wasm-pack builds a valid package for the sourmash crate	1m 24s
test (macos)	1m 27s
Check if cbindgen runs cleanly for generating the C headers	8m 41s
minimum_rust_version	8m 31s
Publish (dry-run)	6m 11s
	1h 2m 15s

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