do not require last statement to be an expression or an instance of DatasetQuery

[skshetry]

This PR removes the requirement for the last statement to be either an expression or an instance of DatasetQuery.

After this PR, scripts without a final expression will function properly in both Datachain and Studio.

The last statement wrappers and related infrastructure will be removed in subsequent PRs.
However, this PR demonstrates that everything already works and is usable.

from datachain.query import DatasetQuery
DatasetQuery("s3://dql-test-e2e", catalog=catalog).save("temp")
print("hello world!")

$ datachain query script.py
Processed: 1 rows [00:00, 512.00 rows/s]
Generated: 9 rows [00:00, 4950.00 rows/s]
Cleanup: 1 tables [00:00, 3498.17 tables/s]
Saving: 279 rows [00:00, 68945.43 rows/s]
hello world!

Part of #360.

[skshetry]

These tests are mocked tests. And since these tests are no longer a failure, they are not useful.

(There is a real test in test_query.py below).

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.72%. Comparing base (a8d3640) to head (638bafe).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #395      +/-   ##
==========================================
- Coverage   86.82%   86.72%   -0.11%     
==========================================
  Files          93       93              
  Lines       10043    10040       -3     
  Branches     2045     2044       -1     
==========================================
- Hits         8720     8707      -13     
- Misses        980      987       +7     
- Partials      343      346       +3     

Flag	Coverage Δ
datachain	86.67% <100.00%> (-0.11%)	⬇️

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[dreadatour]

Looks good to me, thank you! 🙏

We also need to make sure it all works on Studio side (including frontend part).

[skshetry]

Looks good to me, thank you! 🙏

We also need to make sure it all works on Studio side (including frontend part).

It does work well on Studio. We might need to adjust some stuff like "Register dataset" button which is no longer possible as we need explicit saves.

But I'd not consider this as completely functional, that will happen when we completely remove this wrapping thing.

[dreadatour]

Thank you for handling this ❤️