feat:compatible with Pageindex SDK (#238)

* feat:compatible with Pageindex SDK

* corner cases fixed

* fix: mock behavior of old SDK

* fix: close streaming response and warn on empty api_key

- LegacyCloudAPI: close response in `finally` for both _stream_chat_response
  variants so abandoned iterators no longer leak the TCP connection.
- PageIndexClient: emit a warning instead of silently falling back to local
  when api_key is the empty string, surfacing typical env-var-unset misconfig.
- FakeResponse: add close()/closed to match the real requests.Response API.
- Add unit coverage for stream close (both paths) and the empty-api_key warning.
- Add scripts/e2e_legacy_sdk.py to smoke-test the legacy SDK contract end-to-end
  against api.pageindex.ai.

* chore: mark legacy SDK methods with @deprecated and docstring pointers

- Decorate the 12 PageIndexClient cloud-SDK compat methods with
  @typing_extensions.deprecated(..., category=PendingDeprecationWarning):
  - IDE/type-checkers render them with a strikethrough hint
  - runtime warnings stay silent by default (no spam for existing callers),
    surfaceable via `python -W default::PendingDeprecationWarning`
- Add a one-line docstring on each pointing to the Collection-based equivalent.
- Promote typing-extensions to a direct dependency (was transitive via litellm).

---------

Co-authored-by: XinyanZhou <xinyanzhou@XinyanZhoudeMacBook-Pro.local>
Co-authored-by: saccharin98 <xinyanzhou938@gmail.com>
Co-authored-by: mountain <kose2livs@gmail.com>

pyproject.toml

@@ -26,9 +26,11 @@ pymupdf = ">=1.26.0"
 PyPDF2 = ">=3.0.0"
 python-dotenv = ">=1.0.0"
 pyyaml = ">=6.0"
+openai = ">=1.70.0"
 openai-agents = ">=0.1.0"
 requests = ">=2.28.0"
 httpx = {extras = ["socks"], version = ">=0.28.1"}
+typing-extensions = ">=4.9.0"
 
 [tool.poetry.urls]
 Repository = "https://github.com/VectifyAI/PageIndex"