Remove unused [datalib] extra from OpenAI provider base install

[YAshhh29]

The apache-airflow-providers-openai package pulls in the [datalib]
extra of the openai SDK — which transitively installs numpy, pandas,
and pandas-stubs — for every user of this provider. That extra has no
functional use inside this provider today, so it is pure bloat and CVE
noise for anyone installing the provider.

Investigation

I audited every code path that could depend on numpy/pandas reaching
users through this provider:

Check	Location	Result
Provider source	providers/openai/src/**/*.py	0 references to numpy/pandas/DataFrame
Provider unit tests	providers/openai/tests/unit/**	0 references
Provider example DAGs / system tests	providers/openai/tests/system/openai/example_*.py	0 references — only pendulum + Airflow imports
Provider docs	providers/openai/docs/**	Only auto-generated dep tables
Operator return types	operators/openai.py	list[float], str, str | None — no DataFrames
Cross-provider consumers (RAG examples)	providers/{pgvector,pinecone,weaviate}/tests/system/**/example_*_openai.py	pgvector & pinecone: 0 references. weaviate has its own pandas dep declared in providers/weaviate/pyproject.toml
Historical usage	git log providers/openai/pyproject.toml	[datalib] was carried forward across every major version bump (openai 0.x → 1.x → 2.x); recent PR #69068 just bumped openai[datalib]>=1.66.0 → openai[datalib]>=2.37.0 without justifying the extra
Upstream SDK docs	openai/openai-python README (SDK 2.x)	[datalib] is not mentioned anywhere in the modern SDK docs ([aiohttp], [bedrock], [realtime] are — [datalib] is not)

Why it was there in the first place

[datalib] was the extra used by OpenAI SDK 0.x's legacy CLI
(openai tools fine_tunes.prepare_data), which processed JSONL
fine-tuning files via pandas. That CLI was removed when OpenAI SDK 1.x
shipped in 2023, but the extra remained in the package for backward
compatibility. This Airflow provider carried the extra forward across
every subsequent version bump without re-evaluating whether it was
still needed — a classic transitive fossil dependency.

What changes

• providers/openai/pyproject.toml: base dep is now openai>=2.37.0 (no [datalib]); inline comment records the rationale so it doesn't get re-added by the next version bump.
• providers/openai/README.rst and providers/openai/docs/index.rst: dep table updated to reflect the base dep.
• providers/openai/docs/changelog.rst: behavior note under the Changelog header explaining the change and pointing users at pip install 'openai[datalib]' if they had unknowingly relied on the transitive numpy/pandas install for their DAG code.

Impact for users

• Everyone who installs the OpenAI provider stops pulling in numpy, pandas, and pandas-stubs transitively — smaller Docker images, smaller pip-audit surfaces.
• Users of OpenAIHook, OpenAIEmbeddingOperator, OpenAIResponseOperator, and the batch operators are unaffected — none of their code paths use pandas/numpy.
• The one edge case is a user whose DAG code (not the provider) does import pandas and was relying on this provider to bring pandas along transitively. The changelog note points those users at the exact one-line fix.