Add codespell: config, workflow and get it to fix some typos

[yarikoptic]

codespell workflow would just detect when typos introduced, not fix them automagically. Run codespell -w locally to do that. Can use pre-commit to automate. See e.g. https://github.com/dandi/dandi-cli/blob/master/.pre-commit-config.yaml#L21

[jasmainak]

no objection from my end although hnn-core may benefit more from this ;-)