fix: SourceOperator is_source default broken by name mangling

[Ma77Ball]

What changes were proposed in this PR?

Fixes a name-mangling bug in amber/src/main/python/core/models/operator.py.

Operator declared __internal_is_source (double underscore), which Python rewrites per class. So SourceOperator.__internal_is_source = True was stored as _SourceOperator__internal_is_source, while the property kept reading _Operator__internal_is_source. Result: SourceOperator subclasses defaulted to is_source = False, and only worked because ExecutorManager called the setter afterward.

Fix: rename to _internal_is_source (single underscore, no mangling) in Operator's class attribute, getter, setter, and SourceOperator's override. Also removed a dead, mangled line in TableOperator.init.

Any related issues, documentation, or discussions?

Closes: #4736

How was this PR tested?

Updated amber/src/test/python/core/models/test_operator.py:

• Removed the bug-pinning test that asserted on the old mangled attribute names.
• Removed the xfail marker from the contract test, which now passes: SourceOperator() reports is_source is True.

All 29 tests in test_operator.py pass.

Was this PR authored or co-authored using generative AI tooling?

Co-authored with Claude Opus 4.7 in Compliance with ASF

[Ma77Ball]

/request-review @aglinxinyuan

[chenlica]

@Xiao-zhen-Liu Please review it.

[Yicong-Huang]

I still want it to be two underscores as prefix. Is it do able?

[Ma77Ball]

Only if the variable ends in double underline, e.g., --> __internal_is_source__

[Ma77Ball]

Python purposely makes it hard to access, as accessing these types of attribute names outside the class defeats the purpose of encapsulation.

[Yicong-Huang]

yes that's the purpose of using two underscores. I hope to prevent this field from being accessed. but source operator this field should be set to True. can we find a compromise between those requirements?

[Ma77Ball]

There is no way to change how Python handles mangled classes to make this work. However we can just literally spell the mangled name _Operator__internal_is_source = True in SourceOperator. If this is preferred, I can add the change.

[Yicong-Huang]

Let's do it that way for now.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.22%. Comparing base (410c700) to head (9031818).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5007      +/-   ##
============================================
- Coverage     43.22%   43.22%   -0.01%     
  Complexity     2183     2183              
============================================
  Files          1035     1035              
  Lines         38814    38813       -1     
  Branches       4061     4061              
============================================
- Hits          16777    16776       -1     
  Misses        20985    20985              
  Partials       1052     1052              

Flag	Coverage Δ		*Carryforward flag
access-control-service	39.53% <ø> (ø)		Carriedforward from 410c700
agent-service	33.72% <ø> (ø)		Carriedforward from 410c700
amber	43.23% <ø> (ø)		Carriedforward from 410c700
computing-unit-managing-service	0.00% <ø> (ø)		Carriedforward from 410c700
config-service	0.00% <ø> (ø)		Carriedforward from 410c700
file-service	32.18% <ø> (ø)		Carriedforward from 410c700
frontend	34.80% <ø> (ø)		Carriedforward from 410c700
python	88.89% <100.00%> (-0.01%)	⬇️
workflow-compiling-service	47.72% <ø> (ø)		Carriedforward from 410c700

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