Inconsistent docstring format across codebase

Some docstrings use the [google convention](https://github.com/google/styleguide/blob/gh-pages/pyguide.md#383-functions-and-methods): https://github.com/DiamondLightSource/httomo/blob/8a55c4dc62aae97d9d7f4d264602a2cfa96cd23e/httomo/methods.py#L20-L30

whereas other docstrings use the [numpy convention](https://numpydoc.readthedocs.io/en/latest/format.html#parameters): https://github.com/DiamondLightSource/httomo/blob/8a55c4dc62aae97d9d7f4d264602a2cfa96cd23e/httomo/method_wrappers/__init__.py#L20-L58

Picking one convention and sticking with it feels better than having docstrings of various appearances in the source code.