Renamed Compression::Zsld to Compression::Zstd (typo)

[vincev]

I've just noticed the typo while writing a Zstd compressed Parquet.

[codecov-commenter]

Codecov Report

Merging #48 (c0be8c3) into main (1d310ee) will not change coverage.
The diff coverage is 50.00%.

@@           Coverage Diff           @@
##             main      #48   +/-   ##
=======================================
  Coverage   67.64%   67.64%           
=======================================
  Files          64       64           
  Lines        3477     3477           
=======================================
  Hits         2352     2352           
  Misses       1125     1125           

Impacted Files	Coverage Δ
src/parquet_bridge.rs	21.79% <0.00%> (ø)
src/compression.rs	87.87% <100.00%> (ø)

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