Fixed edge cases in writing delta encoder

[jorgecarleitao]

• Deltas need to be encoded from i64 since i32 integers may have a delta >i32::MAX.
• the initial value may need to be set to 0, when the iterator is empty

[codecov-commenter]

Codecov Report

Merging #189 (a9b50b1) into main (a0e66c2) will increase coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #189      +/-   ##
==========================================
+ Coverage   85.71%   85.75%   +0.03%     
==========================================
  Files          84       84              
  Lines        8227     8233       +6     
==========================================
+ Hits         7052     7060       +8     
+ Misses       1175     1173       -2     

Impacted Files	Coverage Δ
src/encoding/delta_bitpacked/encoder.rs	100.00% <100.00%> (ø)
src/encoding/bitpacked/pack.rs	87.87% <0.00%> (-1.52%)	:arrow_down:
src/encoding/bitpacked/mod.rs	74.46% <0.00%> (+3.19%)	:arrow_up:

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