Simplified new signature of growable API

[jorgecarleitao]

It also removes an extra allocation that was being done internally and an extra check.

Backward incompatible changes:

Growable*::new now expects a vector (not slice) of references of their corresponding types and no longer panic (the type is by definition correct). To migrate, downcast the vector of arrays prior to passing them to the growable.

let array = Utf8Array::<i32>::from_iter(vec![Some("a"), Some("bc"), None, Some("defh")]);
let mut a = GrowableUtf8::new(vec![&array], false, 0);

I.e. signature change is new(&[&'a dyn Array], ...) -> new(Vec<&'a A>, ...) where A is the corresponding array type.

[codecov]

Codecov Report

Merging #238 (f271258) into main (3cd8cff) will decrease coverage by 0.02%.
The diff coverage is 76.25%.

@@            Coverage Diff             @@
##             main     #238      +/-   ##
==========================================
- Coverage   76.82%   76.79%   -0.03%     
==========================================
  Files         229      229              
  Lines       19586    19619      +33     
==========================================
+ Hits        15046    15066      +20     
- Misses       4540     4553      +13     

Impacted Files	Coverage Δ
src/compute/filter.rs	63.19% <0.00%> (ø)
src/array/growable/mod.rs	36.23% <45.45%> (+1.53%)	⬆️
src/array/growable/binary.rs	97.29% <100.00%> (-0.08%)	⬇️
src/array/growable/boolean.rs	84.84% <100.00%> (-0.87%)	⬇️
src/array/growable/fixed_binary.rs	86.48% <100.00%> (+2.73%)	⬆️
src/array/growable/list.rs	98.36% <100.00%> (-0.04%)	⬇️
src/array/growable/primitive.rs	100.00% <100.00%> (ø)
src/array/growable/structure.rs	84.25% <100.00%> (ø)
src/array/growable/utf8.rs	100.00% <100.00%> (ø)
src/compute/take/list.rs	100.00% <100.00%> (ø)
... and 2 more

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[ritchie46]

I was thinking about a generic constructor to merge the two into one (in #229), but I do think this better. The caller can be responsible for creating the needed data structure.

As there is already a lifetime in Growable... How do you feel about the following?

pub struct GrowableBinary<'a, 'b, O: Offset> {
    arrays: &'b[&'a BinaryArray<O>>],
    ...
}

Or using the same lifetime 'a for the slice/ Cow (in case of ownership problems).

[jorgecarleitao]

I agree that we can further simplify this. Would it be ok to leave it to a next iteration? I think I need to think about this a bit more: it seems to me that we do not even need the Vec in all cases for as long as we internally allocate references to the supporting buffers and validities. It needs a small internal refactor, but it might work.