Fix off-by-one error in delta-bitpacked decoder

[kornholi]

This fixes an off-by-one error not accounting for the initial value
present in the header, causing an extra (unused) delta to be read at the
end. In most cases it wasn't an issue as there's padding in the blocks.

[codecov-commenter]

Codecov Report

Merging #66 (b88d4c7) into main (b0a6296) will decrease coverage by 0.05%.
The diff coverage is 93.10%.

@@            Coverage Diff             @@
##             main      #66      +/-   ##
==========================================
- Coverage   69.21%   69.16%   -0.06%     
==========================================
  Files          66       66              
  Lines        3677     3661      -16     
==========================================
- Hits         2545     2532      -13     
+ Misses       1132     1129       -3     

Impacted Files	Coverage Δ
src/encoding/delta_bitpacked/decoder.rs	94.78% <93.10%> (+1.64%)	⬆️
src/schema/types/physical_type.rs	91.30% <0.00%> (-4.35%)	⬇️
src/schema/io_thrift/from_thrift.rs	85.18% <0.00%> (-2.09%)	⬇️
src/metadata/schema_descriptor.rs	66.66% <0.00%> (-1.97%)	⬇️
src/read/metadata.rs	73.56% <0.00%> (-1.44%)	⬇️
src/schema/io_message/from_message.rs	81.59% <0.00%> (-0.76%)	⬇️
src/read/page_iterator.rs	83.33% <0.00%> (-0.39%)	⬇️
src/read/compression.rs	80.00% <0.00%> (-0.29%)	⬇️
integration-tests/src/read/primitive_nested.rs	79.54% <0.00%> (-0.23%)	⬇️
src/lib.rs	80.16% <0.00%> (-0.09%)	⬇️
... and 11 more

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