Patch: copy var lists and strings

[ray6080]

Two fixes:

• indices column chunk is not initialized with correct capacity;
• ColumnChunks are reused during copy rel, but we didn't reset column chunk's buffer during resetToEmpty. Now we leave gaps in rel csr arrays, and gapped values will be filled with old data from previous "chunks", and this can corrupt finalize for strings. (index can be insane values, leading to out-of-bound read from dictionary chunk).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b61758e) 93.49% compared to head (4ee6ed3) 93.49%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2928   +/-   ##
=======================================
  Coverage   93.49%   93.49%           
=======================================
  Files        1116     1116           
  Lines       42716    42717    +1     
=======================================
+ Hits        39936    39938    +2     
+ Misses       2780     2779    -1     

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