Update the import to DataChain and C to functional

[amritghimire]

• Fix imports for tests
• Fix imports in examples and other files

Sorry for making you review this changes for 66 files./

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[codecov]

Codecov Report

Attention: Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.09%. Comparing base (212edb1) to head (db6cd08).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/datachain/cli/commands/show.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #995      +/-   ##
==========================================
- Coverage   88.34%   88.09%   -0.26%     
==========================================
  Files         145      145              
  Lines       12280    12279       -1     
  Branches     1699     1699              
==========================================
- Hits        10849    10817      -32     
- Misses       1014     1045      +31     
  Partials      417      417              

Flag	Coverage Δ
datachain	88.02% <90.47%> (-0.26%)	⬇️

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