base
test unify::test::big_array_bench ... bench:   1,416,793 ns/iter (+/- 216,475)

assert -> debug_assert
test unify::test::big_array_bench ... bench:   1,420,368 ns/iter (+/- 144,433)
test unify::test::big_array_bench ... bench:   1,414,448 ns/iter (+/- 219,137)

don't copy for redirects
test unify::test::big_array_bench ... bench:   1,349,796 ns/iter (+/- 233,931)
test unify::test::big_array_bench ... bench:   1,367,082 ns/iter (+/- 301,644)
test unify::test::big_array_bench ... bench:   1,358,154 ns/iter (+/- 348,796)

copy less
test unify::test::big_array_bench ... bench:     744,775 ns/iter (+/- 51,865)
test unify::test::big_array_bench ... bench:     750,939 ns/iter (+/- 146,417)
test unify::test::big_array_bench ... bench:     754,104 ns/iter (+/- 121,968)

s/set-value/update-value/
test unify::test::big_array_bench ... bench:     731,531 ns/iter (+/- 125,685)
test unify::test::big_array_bench ... bench:     725,162 ns/iter (+/- 99,013)
test unify::test::big_array_bench ... bench:     735,473 ns/iter (+/- 121,156)
