Fix for reading exported parquet

[ilongin]

Fixing the issue when we read parquet file that is being created with datachain itself and already has source fields inside it. What was happening is that we were adding duplicated source fields on read and this PR avoids that even if source=True flag is set.

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[shcheklein]

@ilongin tests are broken?

@ilongin should we actually rewrite source if source is True? 🤔 since the existing source is kinda wrong by now ...

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.69%. Comparing base (ff97825) to head (e560b08). Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1071   +/-   ##
=======================================
  Coverage   88.68%   88.69%           
=======================================
  Files         152      152           
  Lines       13606    13609    +3     
  Branches     1893     1894    +1     
=======================================
+ Hits        12067    12070    +3     
  Misses       1093     1093           
  Partials      446      446           

Flag	Coverage Δ
datachain	88.62% <100.00%> (+<0.01%)	:arrow_up:

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Files with missing lines	Coverage Δ
src/datachain/lib/arrow.py	98.80% <100.00%> (+0.02%)	:arrow_up:

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[ilongin]

@ilongin should we actually rewrite source if source is True? 🤔 since the existing source is kinda wrong by now ...

Make sense, I've overwritten it now with new source.

[shcheklein]

@ilongin what is the status here?