build(poetry): use new (parallel) installer

[prusnak]

We've been sticking to the old poetry installer because of python-poetry/poetry#3199

But it seems the issue is gone now (fixed in poetry 1.1.6) and we can use the new (parallel) installer again.

Change was introduced in #1436 and this PR reverts it

machine	before	after
Intel Xeon Desktop	$ time poetry shell ... real 2m11.478s user 1m43.056s sys 0m9.334s	$ time poetry shell ... real 0m32.622s user 2m26.914s sys 0m12.072s
Macbook Air M1	$ time poetry install ... real 1m13.131s user 0m52.100s sys 0m7.698s	$ time poetry install ... real 0m22.092s user 1m14.373s sys 0m12.048s

Obviously we'd need to test in the CI several times to be sure this works.

[matejcik]

don't we need to update poetry in nix-shell for this?

[prusnak]

don't we need to update poetry in nix-shell for this?

No, we don't. We have poetry 1.1.13 there already, since we updated shell.nix in June - 0112d01. I was testing this PR using that version of poetry.

Btw, nixpkgs-unstable has poetry 1.2.2, I retested using that version:

machine	before	after
Macbook Air M1	$ time poetry install ... real 0m57.129s user 0m37.231s sys 0m7.398s	$ time poetry install ... real 0m21.188s user 1m8.152s sys 0m14.383s

The improvement is still significant for poetry 1.2.x.

[matejcik]

ok then