fix invalid parquet read

[ritchie46]

fixes #1329

The length of the offsets container return n - 1. This is unintuitive and lead to a bug where the extend_constant added a single value too little. I made the distinction between len (the real number of indexes) and len_proxy the number of values an array with this many offsets would have.

[codecov]

Codecov Report

Base: 83.12% // Head: 83.11% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (ba2c79b) compared to base (1fcfd7c).
Patch coverage: 70.58% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1330      +/-   ##
==========================================
- Coverage   83.12%   83.11%   -0.02%     
==========================================
  Files         370      370              
  Lines       40169    40172       +3     
==========================================
- Hits        33391    33388       -3     
- Misses       6778     6784       +6     

Impacted Files	Coverage Δ
src/io/avro/read/nested.rs	61.21% <50.00%> (ø)
src/offset.rs	84.36% <50.00%> (-0.94%)	⬇️
src/io/parquet/read/deserialize/binary/utils.rs	65.30% <66.66%> (ø)
src/array/binary/mutable_values.rs	76.47% <100.00%> (ø)
src/array/list/mutable.rs	79.89% <100.00%> (ø)
src/array/physical_binary.rs	94.67% <100.00%> (ø)
src/array/utf8/mutable_values.rs	83.06% <100.00%> (ø)
src/array/binary/mod.rs	90.07% <0.00%> (-1.15%)	⬇️

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[jorgecarleitao]

Agree that it is a bit confusing - I was also not sure about what to use. This addresses it indeed ^^