Extract duplicated thread_id fallback logic from 11 files into a single
deerflow.utils.runtime.get_thread_id() function with a documented 3-level
cascade (runtime.context → runtime.config → get_config()).
The module docstring also clarifies the __pregel_runtime injection pattern used in
gateway mode.
* Fix Windows backend test compatibility
* Preserve ACP path style on Windows
* Fix installer import ordering
* Address review comments for Windows fixes
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>