refactor!: remove gevent runtime dependency in v0.10.0

[WH-2099]

Background

0.9.0 still depends on gevent and applies it at import time. For 0.10.0, we should make this an explicit breaking cleanup: remove the greenlet-based runtime path, keep synchronous plugin execution simple, and prepare the SDK for an asyncio-first direction.

This should be a root fix, not a compatibility shim around the current global patching model.

Current state

• pyproject.toml declares direct runtime dependencies on gevent>=26.4.0 and requests>=2.33.1.
• src/dify_plugin/__init__.py imports src/dify_plugin/_gevent.py, which runs monkey.patch_all(sys=True) as a package import side effect.
• Runtime readers still contain gevent-specific paths:
  • src/dify_plugin/core/server/stdio/request_reader.py uses gevent.os.tp_read.
  • src/dify_plugin/core/server/tcp/request_reader.py uses gevent.socket, gevent.select.select, and gevent.sleep.
  • src/dify_plugin/core/server/serverless/request_reader.py uses gevent.pywsgi.WSGIServer when sockets are patched.
• src/dify_plugin/interfaces/model/ai_model.py detects patched sockets and uses gevent.threadpool.ThreadPool for token estimation.
• src/dify_plugin/core/server/io_server.py already dispatches sync plugin work through ThreadPoolExecutor(max_workers=MAX_WORKER), which is the simpler concurrency primitive for IO-heavy plugins.
• SDK-owned HTTP paths still use requests, including file invocation and OpenAI-compatible model implementations. Examples also use requests, but those are plugin-local dependencies and can be handled as a separate migration surface if needed.

Target for v0.10.0

• Remove gevent and greenlet from SDK runtime dependencies and lock data.
• Remove package import-time patching entirely.
• Keep sync plugin execution on ThreadPoolExecutor; tune defaults/documentation around IO-heavy workloads instead of greenlet concurrency.
• Replace SDK-owned requests usage with a small urllib.request based helper for JSON requests, streaming responses, headers, timeouts, upload payloads, and HTTP error mapping.
• Keep the existing protocol surfaces working:
  • local stdio
  • remote TCP
  • serverless HTTP streaming
• Shape the runtime boundaries so later asyncio-native readers/writers can be introduced without another global monkey-patching layer.

Proposed work

• Delete the import side-effect module and remove the package-level import.
• Rewrite stdio reading around standard library primitives.
• Rewrite TCP reading/writing around native sockets and selectors or select, with explicit timeout/reconnect behavior.
• Replace the serverless gevent WSGI branch with the simplest supported non-gevent server path for this SDK release.
• Replace model token-estimation isolation with either direct execution or a standard ThreadPoolExecutor, depending on blocking impact.
• Add a small internal HTTP helper built on urllib.request; migrate SDK runtime call sites away from requests.
• Update config defaults/descriptions that currently mention gevent worker behavior.
• Update docs and examples that describe the runtime model.
• Add regression tests for import side effects, stdio/TCP/serverless readers, HTTP error mapping, streaming, and thread-pool execution.

Acceptance criteria

• rg -n "gevent|greenlet" src pyproject.toml returns no runtime references.
• rg -n "requests" src pyproject.toml returns no SDK runtime references.
• just check passes.
• just test passes.
• Local, remote TCP, and serverless smoke paths still run without global monkey patching.
• The release notes for 0.10.0 call out this as a breaking runtime migration.