Add a reset API

[LaurenzV]

This allows users to reset chunks, making it possible to reuse the inner allocations. While I don't have a specific need for this now, I think it could come in handy in the future.

I'm not sure if the reset method should take Settings as well so that they can be changed if desired. Or maybe a reset_with_settings method?

[saecki]

Maybe the settings could be changed arbitrarily, then the combinations of constructors could be reduced and instead a builder method and a setter (and even a getter?) could be exposed.

[laurmaedje]

I'm fine with this, but would try avoid it taking Setting or having reset_with_settings. Maybe a builder style API would work, but that could be looked into separately.

CI is failing though due to formatting.

[saecki]

A separate bulider type could be circumvented if we allow changing the Settings arbitrarily, which I think would be nice anyway, because then it could just be an inherent method on Chunk.

But yeah, that doesn't need to happen in this PR :)