fix: merge streaming tool deltas by logical index

[FU-max-boop]

Summary

Fixes #3201.

• Collapse duplicate indexed list deltas in the initial streaming chunk before storing them in the accumulator.
• Merge later indexed entries by their logical index field, with positional fallback for full Assistants snapshots that omit the delta-only index.
• Reuse the chat streaming delta accumulator from Assistants streaming so both paths share the fix.

The branch is rebased onto the current main; the Assistants import conflict was resolved while preserving the current timeout handling.

Validation

• pytest tests/lib/test_streaming_deltas.py tests/lib/chat/test_completions_streaming.py -q -o addopts="" — 17 passed
• ruff check src/openai/lib/streaming/_deltas.py src/openai/lib/streaming/_assistants.py tests/lib/test_streaming_deltas.py
• ruff format --check src/openai/lib/streaming/_deltas.py src/openai/lib/streaming/_assistants.py tests/lib/test_streaming_deltas.py
• scripts/run-pyright src/openai/lib/streaming/_deltas.py src/openai/lib/streaming/_assistants.py tests/lib/test_streaming_deltas.py
• git diff --check

[FU-max-boop]

Rebased this fix onto the current main and resolved the Assistants import conflict while preserving the newer timeout handling. The focused streaming suite is green (17 tests), and Ruff, Pyright, formatting, and diff checks all pass.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

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[marcuswood-oai]

Thanks for taking the time to work on this! We’ve merged the fix for duplicate-index tool-call deltas in #3425, so I’m closing this as a duplicate. We appreciate the contribution.