Use par files to execute targets

[prebeta]

In order to ensure an encapsulated execution environment, we can use par files here to ensure that things work properly here in all our environments. We ran into issues where the locally installed version of pip was leaking into the piptool.py script and caused build breakages.

https://app.asana.com/0/0/1164576901785385/f

[ali5h]

thank you, fyi, par files are not a good option for a public repo, they are basically binary files checked into repo, and updating them is not straight forward. we specifically removed par files because of this

[ali5h]

check this too bazelbuild/rules_python#184

[prebeta]

Thanks for the context! I accidentally opened the PR on the wrong repository.

I agree that having to manage checked-in binaries is not an ideal solution and it's cleaner to directly execute on the source code, but some old installations of pip seem to leak into the execution environment here and cause import issues.

I'll maintain this code in our own repo for now.