Work towards `Batcher` unification #469

Job	Run time
test mdBook	40s
cargo test on ubuntu, rust stable	53s
cargo test on ubuntu, rust 1.78	1m 9s
cargo test on macos, rust stable	1m 10s
cargo test on macos, rust 1.78	1m 5s
cargo test on windows, rust stable	2m 41s
cargo test on windows, rust 1.78	2m 4s
	9m 42s

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