Hall kernel

[jbarr444]

Added a collision kernel which interpolates the table from Hall 1980.

[slayoo]

@jbarr444, the key prerequisite for any PR is a unit test.
Here, we have the table from the paper that can serve as a source for expected values.
We use the pytest framework for unit testing, here's an example tutorial: https://betterstack.com/community/guides/testing/pytest-guide/
In short, we need a function (named test_... to be discoverable by pytest) that includes an arrange-act-assert logic, in which a minimal setup (the "arrange" part) to use the new code would be executed (the "act" part), and the results obtained by the newly introduced unit would be checked against dome reference values (the "assert" part).