fix: types and documentation improvements

[cjumel]

Description

The main addition of this PR is a small set of improvments/fixes on types and code documentation (d811833), with the goal of making the docstrings and the types more accurate, remove unecessary ones and prepare for future API changes.

Then, I work on a few minor fixes, namely the PR template, which got out-of-date, and the python version.

Besides this, I made some work on standardazing this repository configs with other repositories we have at Linkup, which concretely means:

• enable the standard rules we use (formatters or type checker setting for instance)
• import the missing config files from our template repository

Since they are a lot of small changes in this PR, it might be easier to review it commit by commit.

Checklist

• I have run the tests locally with make install-dev and make test
• I have updated the README.md if my changes affected it
• I have updated the package version in linkup/_version.py and pyproject.toml if I plan on creating a new release

[vlapparov]

LGTM. One comment left- optional to address. Great job

[vlapparov]

LGTM