fix(partition): avoid copying spooled uploads

[CyMule]

Summary

• Reuse SpooledTemporaryFile uploads directly on supported Python versions.
• Rewind spooled streams before passing them to downstream consumers.
• Remove document-sized BytesIO copies from DOCX and PPTX partitioning.
• Update regression tests to verify that the original stream is reused.

Why

Python 3.11 and newer provide the buffered-I/O methods required by zipfile and other consumers. Converting a spooled upload to BytesIO therefore adds a document-sized heap allocation without providing compatibility value.

This change removes that allocation without introducing a file-size limit or changing the partition API.

Impact

In a representative end-to-end partition API benchmark using a 54.9 MB DOCX upload:

• Peak process RSS decreased by 51.2 MiB.
• Peak container memory decreased by 52.6 MiB.
• Median latency changed from 9.343s to 9.197s (-1.6%).

This removes approximately one document-sized allocation without a measured performance penalty.

Validation

• Focused common, DOCX, and PPTX tests — 3 passed.
• uv run ruff check unstructured/partition/common/common.py unstructured/partition/docx.py unstructured/partition/pptx.py test_unstructured/partition/common/test_common.py test_unstructured/partition/test_docx.py test_unstructured/partition/test_pptx.py — passed.