Added support to read Avro's structs

[jorgecarleitao]

Also simplified some internal code

[codecov]

Codecov Report

Merging #826 (100677b) into main (d8093bf) will increase coverage by 0.06%.
The diff coverage is 54.28%.

@@            Coverage Diff             @@
##             main     #826      +/-   ##
==========================================
+ Coverage   71.60%   71.67%   +0.06%     
==========================================
  Files         326      326              
  Lines       17516    17640     +124     
==========================================
+ Hits        12543    12644     +101     
- Misses       4973     4996      +23     

Impacted Files	Coverage Δ
src/io/avro/read/nested.rs	38.93% <31.42%> (-5.51%)	⬇️
src/io/avro/read/schema.rs	69.62% <69.23%> (+11.39%)	⬆️
src/io/avro/read/deserialize.rs	74.30% <81.81%> (-0.50%)	⬇️
src/bitmap/utils/slice_iterator.rs	87.93% <0.00%> (+1.72%)	⬆️
src/io/avro/write/serialize.rs	89.20% <0.00%> (+3.28%)	⬆️

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