Add async save path, pinned-pool coalescing, and Python bindings for KVortexEngine

[fantasy520]

Motivation

• Expose a safe Python API for KVortex and make block/hasher conversions convenient for bindings using pybind11.
• Add asynchronous save support to avoid blocking callers and provide handles to wait on background saves via save_blocks_async/wait.
• Improve PinnedHostPool free-list handling by supporting coalescing to avoid fragmentation regressions.

Description

• Added Python bindings in bindings.cpp to expose KVortexConfig, CacheStats, KVortexEngine, and BlockHasher, including helpers to convert BlockID to/from py::bytes and map KVortexError to std::runtime_error exceptions, and provided alias attributes Config and Stats for backwards compatibility.
• Implemented a real async save mechanism in KVortexEngine (include/kvortex/api/kvortex.hpp and src/api/kvortex.cpp) with AsyncSaveTask, an async worker thread (async_worker_loop), queuing (async_queue_), result tracking (async_results_), save_blocks_async that copies payloads into task buffers, and a blocking wait that returns errors from background work; the worker is started in create and joined on shutdown.
• Disabled move semantics for KVortexEngine by deleting the move ctor/assignment to avoid thread/ownership issues introduced by the background worker thread.
• Implemented PinnedHostPool improvements in include/kvortex/memory/pool.hpp and src/memory/pool.cpp: maintain free_blocks_by_offset_ to allow coalescing, added helper methods insert_free_block/remove_free_block, and perform coalescing on deallocate; updated allocation/deallocation logic to use the helpers.
• Minor includes and utility helpers added (<cstring>, <mutex>, <thread>, <condition_variable>) where needed.

Testing

• Ran the unit/integration test suite with GoogleTest targeting memory and integration scenarios: tests/test_memory.cpp (including PinnedHostPool.CoalescingRegression) and tests/test_integration.cpp (including Integration.SaveBlocksAsyncWait), and all tests passed.
• Verified that the new Python bindings build (CI-style compilation) and the async path correctly reports background errors via wait in the added integration test.

---

Codex Task

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 6f566ba1e2

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Move coalescing index when moving PinnedHostPool

The new free_blocks_by_offset_ map is now required for deallocate coalescing, but the existing move constructor/assignment in src/memory/pool.cpp still only transfer free_blocks_ and allocated_blocks_. Because moves are public on PinnedHostPool, moving a pool leaves this offset index out of sync/empty in the destination object, so adjacent free regions stop coalescing and long-running workloads can hit avoidable fragmentation and out-of-memory errors after a move.

Useful? React with 👍 / 👎.