Add custom pygrep QAQC tooling

[VeckoTheGecko]

Look into custom pygrep linting.

We can add custom QAQC pre-commit rules to Parcels to enforce internal conventions. Ones I have in mind:

instead of

from parcels.convert import nemo_to_sgrid

nemo_to_sgrid(...)

use

import parcels

parcels.convert.nemo_to_sgrid(...)

# or
from parcels import convert
convert.nemo_to_sgrid(...)

instead of

from parcels._typing import Mesh #etc.

Mesh

use

import parcels._typing as ptyping # enforce the ptyping alias

ptyping.Mesh

[VeckoTheGecko]

(note that I haven't seen another project that does this. So this may indeed be a bit "extra")