Fix incorrect downcast in estimated_size_bytes

[jleibs]

Looks like this might have been a copy-and-paste error?

Added a unit-test for fixed_size_list as well.

[ritchie46]

Thanks you @jleibs 👍

[codecov]

Codecov Report

Base: 83.19% // Head: 83.18% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (704c4e3) compared to base (26d1b11).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1351      +/-   ##
==========================================
- Coverage   83.19%   83.18%   -0.01%     
==========================================
  Files         371      371              
  Lines       40304    40304              
==========================================
- Hits        33529    33528       -1     
- Misses       6775     6776       +1     

Impacted Files	Coverage Δ
src/compute/aggregate/memory.rs	39.28% <100.00%> (+3.57%)	⬆️
src/array/binary/mod.rs	90.94% <0.00%> (-1.19%)	⬇️
src/io/ipc/read/file.rs	96.42% <0.00%> (-0.45%)	⬇️
src/offset.rs	84.89% <0.00%> (+0.35%)	⬆️

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[jorgecarleitao]

Thanks a lot, @jleibs !