Fix field renames after external class data writes

[yangfan-yf-yf]

Description

After Box.slot = Value(), renaming Value.field can leave Box.slot.field unchanged and break execution. I track a single unconditional module-level data assignment when both classes are defined in the same module with unique bindings, including replacement of an existing attribute. I preserve the original import source identity separately from the replacement attribute value.

I reject affected renames before producing changes when earlier reads, rebinding, repeated or conditional writes, inheritance, or lookup hooks make the value uncertain. Callable and descriptor assignments, general dynamic/factory inference, and arbitrary containers remain outside this support.

I added regression controls for imported factories, module aliases and cycles, nested classes, namespace modules, Unicode import offsets, and local pattern/exception/unpacking rebinding. A potentially affected field rename must preserve execution or refuse changes atomically; an unrelated global rename and an ordinary referenced field rename must still succeed.

I validated the current change locally:

• The complete Python 3.12 suite: 2242 passed, 12 skipped, 5 xfailed (2259 collected).
• All 93 regression cases passed on both Python 3.12 and 3.14.
• The 303 focused compatibility cases with Preserve annotation, lambda and comprehension source bindings #900: 288 passed/15 skipped on 3.12 and 286 passed/17 skipped on 3.14. This is the selected integration scope.
• Black, isort and the configured checks passed.

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have updated CHANGELOG.md
• I have made corresponding changes to user documentation for new features

[codecov]

Codecov Report

❌ Patch coverage is 96.02220% with 43 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.39%. Comparing base (22f5e50) to head (a6da74e).

Files with missing lines	Patch %	Lines
rope/base/externaldata.py	92.14%	40 Missing ⚠️
ropetest/external_data_attributes_test.py	99.46%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #901      +/-   ##
==========================================
+ Coverage   95.34%   95.39%   +0.04%     
==========================================
  Files         134      136       +2     
  Lines       26762    27843    +1081     
==========================================
+ Hits        25516    26560    +1044     
- Misses       1246     1283      +37     

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