rename to_arrow, as_arrow

[andrewgazelka]

In the codebase, we have two methods: to_arrow and as_arrow. These can be potentially confusing due to uncertainty regarding when to use each one. It would be useful to add documentation or perhaps even unify the methods or create a new method that returns a Cow.

The reason for this is that to_arrow performs an allocation, whereas as_arrow returns a reference. Sometimes, you don't actually need to do the allocation. If you return a Cow, it can either avoid allocation by returning Cow::Borrowed, or perform an allocation when necessary and return Cow::Owned.

[universalmind303]

there are lots of to_arrow methods in the codebase, can you provide more info on which ones you are suggesting changing