Fix inline image reuse after merging image-bearing subdoc

[ahmetmusab42-stack]

Summary

• normalize only the matching copied-image wrapper when an InlineImage reuses an image already introduced by docxcompose;
• preserve the existing fast path and unrelated image/error behavior;
• add regression coverage for path and BytesIO descriptors, repeated rendering, image deduplication, and an unsupported-image subdocument.

Root cause

When a subdocument contributes an image, docxcompose can cache that image part with its lightweight ImageWrapper. If a later InlineImage has the same bytes, python-docx reuses the part and expects the returned image object to implement scaled_dimensions(). The wrapper does not, so rendering raises AttributeError.

The fix replaces only the checksum-matching wrapper with a native python-docx Image before the normal new_pic_inline() path runs. It does not monkey-patch third-party classes or catch broad exceptions.

Verification

• reproduced can not insert a inline image and a subdoc with an image #474 on current master with the reporter's template1.docx, template2.docx, and index.jpeg;
• verified those exact fixtures render with this change;
• new regression script passed on Python 3.9, 3.10, 3.13, and 3.14 with python-docx 1.2.0 / docxcompose 2.2.0;
• legacy combination passed with python-docx 1.1.2 / docxcompose 1.4.1;
• 37 existing direct test scripts passed;
• Flake8, git diff --check, sdist, and wheel builds passed.

Fixes #474.

OpenAI Codex assisted with reproduction, implementation, and test execution. I reviewed the diff and verification results and remain responsible for this contribution.