Work towards `Batcher` unification #476

Job	Run time
test mdBook	39s
cargo test on ubuntu, rust stable	42s
cargo test on ubuntu, rust 1.78	53s
cargo test on macos, rust stable	43s
cargo test on macos, rust 1.78	55s
cargo test on windows, rust stable	2m 15s
cargo test on windows, rust 1.78	1m 50s
	7m 57s

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