both for Autocorrelate and AutocorrelateMP, even though for the latter
the change only covers converting the divisor expression as a whole,
instead of individual elements separately.
also, update .pre-commit-config.yaml to:
* first change to ./p2, then run the tests (pre-commit deliberately does
not allow this by design [1])
* for the above, the https://github.com/dnephin/pre-commit-golang repo
had to be dropped as it does not allow any customisation either.
also, add some flake updates (would be better split into another commit,
I know):
* use baseurl var
* add statix to shell packages
* fix building p1
refs:
[1]: https://github.com/pre-commit/pre-commit/issues/1110
