update _process_stream to resolve PytestUnhandledThreadExceptionWarnings

[EdwardLi-coder]

I encounter many PytestUnhandledThreadExceptionWarnings coming from the _process_stream function, so I optimized the method.
This is the warning.

tests/func/test_catalog.py::test_query[file-False-tree0]
  /Users/lifei/PycharmProjects/datachain/.nox/tests-3-12/lib/python3.12/site-packages/_pytest/threadexception.py:82: PytestUnhandledThreadExceptionWarning: Exception in thread Thread-2 (_process_stream)
  
  Traceback (most recent call last):
    File "/opt/miniconda3/envs/datachain/lib/python3.12/threading.py", line 1075, in _bootstrap_inner
      self.run()
    File "/opt/miniconda3/envs/datachain/lib/python3.12/threading.py", line 1012, in run
      self._target(*self._args, **self._kwargs)
    File "/Users/lifei/PycharmProjects/datachain/.nox/tests-3-12/lib/python3.12/site-packages/datachain/catalog/catalog.py", line 118, in _process_stream
      buffer += byt
  TypeError: can't concat str to bytes
  
    warnings.warn(pytest.PytestUnhandledThreadExceptionWarning(msg))

[codecov]

Codecov Report

Attention: Patch coverage is 64.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 87.13%. Comparing base (d6a29df) to head (ac7ecc3).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/datachain/catalog/catalog.py	64.00%	5 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #433      +/-   ##
==========================================
- Coverage   87.17%   87.13%   -0.05%     
==========================================
  Files          92       92              
  Lines        9975     9989      +14     
  Branches     2053     2057       +4     
==========================================
+ Hits         8696     8704       +8     
- Misses        926      929       +3     
- Partials      353      356       +3     

Flag	Coverage Δ
datachain	87.08% <64.00%> (-0.05%)	⬇️

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[skshetry]

@EdwardLi-coder, thanks for creating this PR, but this was fixed by #431. Please rebase/pull the latest main branch. :)

[EdwardLi-coder]

@EdwardLi-coder, thanks for creating this PR, but this was fixed by #431. Please rebase/pull the latest main branch. :)

ok