Remove `'static` requirement from difference traits #323

Job	Run time
test mdBook	43s
cargo test on ubuntu, rust stable	55s
cargo test on ubuntu, rust 1.78	1m 2s
cargo test on macos, rust stable	2m 29s
cargo test on macos, rust 1.78	1m 50s
cargo test on windows, rust stable	2m 36s
cargo test on windows, rust 1.78	1m 41s
	11m 16s

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