feat: stability improvements, see detail below

Key stability improvements made (deterministic + bounded)
1) Bounded memory usage in long-running stats
Fixed unbounded growth in NetworkState latency tracking:
Replaced std::vector<uint16_t> m_latency + push_back() with a fixed-size ring buffer (kLatencyWindow = 1024) and explicit counters.
Median latency computation now operates on at most 1024 samples, preventing memory growth and avoiding performance cliffs from ever-growing copies/sorts.
2) Prevent crash/UAF on shutdown + more predictable teardown
Controller shutdown ordering (Controller::stop()):
Now stops m_miner before destroying m_network.
This reduces chances of worker threads submitting results into a network listener that’s already destroyed.
Thread teardown hardening (backend/common/Thread.h):
Destructor now checks std:🧵:joinable() before join().
Avoids std::terminate() if a thread object exists but never started due to early exit/error paths.
3) Fixed real leaks (including executable memory)
Executable memory leak fixed (crypto/cn/CnCtx.cpp):
CnCtx::create() allocates executable memory for generated_code via VirtualMemory::allocateExecutableMemory(0x4000, ...).
Previously CnCtx::release() only _mm_free()’d the struct, leaking the executable mapping.
Now CnCtx::release() frees generated_code before freeing the ctx.
GPU verification leak fixed (net/JobResults.cpp):
In getResults() (GPU result verification), a cryptonight_ctx was created via CnCtx::create() but never released.
Added CnCtx::release(ctx, 1).
4) JobResults: bounded queues + backpressure + safe shutdown semantics
The old JobResults could:

enqueue unlimited std::list items (m_results, m_bundles) → unbounded RAM,
call uv_queue_work per async batch → unbounded libuv threadpool backlog,
delete handler directly while worker threads might still submit → potential crash/UAF.
Changes made:

Hard queue limits:
kMaxQueuedResults = 4096
kMaxQueuedBundles = 256
Excess is dropped (bounded behavior under load).
Async coalescing:
Only one pending async notification at a time (m_pendingAsync), reducing eventfd/uv wake storms.
Bounded libuv work scheduling:
Only one uv_queue_work is scheduled at a time (m_workScheduled), preventing CPU starvation and unpredictable backlog.
Safe shutdown:
JobResults::stop() now detaches global handler first, then calls handler->stop().
Shutdown detaches m_listener, clears queues, and defers deletion until in-flight work is done.
Defensive bound on GPU result count:
Clamp count to 0xFF inside JobResults as well, not just in the caller, to guard against corrupted kernels/drivers.
5) Idempotent cleanup
VirtualMemory::destroy() now sets pool = nullptr after delete:
prevents accidental double-delete on repeated teardown paths.
Verification performed
codespell . --config ./.codespellrc: clean
CMake configure + build completed successfully (Release build)

Signed-off-by: rezky_nightky <with.rezky@gmail.com>

src/backend/common/Thread.h

@@ -65,7 +65,7 @@ public:
         }
     }
 #   else
-    inline ~Thread() { m_thread.join(); delete m_worker; }
+    inline ~Thread() { if (m_thread.joinable()) { m_thread.join(); } delete m_worker; }
 
     inline void start(void *(*callback)(void *))    { m_thread = std::thread(callback, this); }
 #   endif