* Cleanup redundant code
* Use a type alias to make sure the `caster_query` and
`not_caster_query` really do the same thing and access the same things
**Objective**
Cleanup code that would otherwise be difficult to understand
**Solution**
* `extract_meshes` had two for loops which are functionally identical,
just copy-pasted code. I extracted the common code between the two
and put them into an anonymous function.
* I flattened the tuple literal for the bundle batch, it looks much
less nested and the code is much more readable as a result.
* The parameters of `extract_meshes` were also very daunting, but they
turned out to be the same query repeated twice. I extracted the query
into a type alias.
EDIT: I reworked the PR to **not do anything breaking**, and keep the old allocation behavior. Removing the memorized length was clearly a performance loss, so I kept it.
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