Fixed panic in deserializing nested statistics

[jorgecarleitao]

When deserializing nested statistics from parquet, we need to take into account that the null count of a List[Struct] can't be UInt64 and should instead be something like List[{"a": null_a, "b": null_b}]. This PR fixes this.

I think we can still improve this a bit (e.g. why not {"a": null_a, "b": null_b} instead?) so that users can use nested statistics to create predicates for filter pushdown of nested types, but at least this no longer panics.

[codecov]

Codecov Report

Merging #1139 (d67dc12) into main (b3583b6) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1139      +/-   ##
==========================================
+ Coverage   83.49%   83.51%   +0.02%     
==========================================
  Files         366      366              
  Lines       35635    35691      +56     
==========================================
+ Hits        29752    29808      +56     
  Misses       5883     5883              

Impacted Files	Coverage Δ
src/io/parquet/read/statistics/mod.rs	93.68% <100.00%> (+1.03%)	⬆️
src/io/ipc/read/reader.rs	95.84% <0.00%> (-0.70%)	⬇️
src/bitmap/immutable.rs	84.56% <0.00%> (+0.61%)	⬆️
src/bitmap/utils/slice_iterator.rs	98.78% <0.00%> (+1.21%)	⬆️

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