lib/std: better policy for enlarging HashCollection

Signed-off-by: Jean Privat <jean@pryen.org>
lib/std: improve implementation of `Set.hash` and `Sequence.hash`

Signed-off-by: Jean Privat <jean@pryen.org>
tests: update sav because line changes in standard::array

Signed-off-by: Jean Privat <jean@pryen.org>