Android native: tighten Oboe build, fix getLastError race, cut audio-thread syscalls - #208

Follow-up to the Oboe/Veldrid integration: apply the deferred optimizations from the previous PR and harden one race-y P/Invoke path discovered on a second pass. No game logic touched.

CMake (osu.Android/Native/CMakeLists.txt)

• Strip -ffast-math from Oboe's compile options (kept on our own bridge). Avoids __FINITE_MATH_ONLY__ symbol-version drift against system libm.
• OBOE_BUILD_TESTS / EXAMPLES / DOCS = OFF and BUILD_TESTING = OFF — FetchContent stops compiling artifacts we never ship.
• GIT_SHALLOW TRUE on the Oboe FetchContent_Declare for faster CI checkout.

Audio bridge (oboe_bridge.{h,cpp})

• Explicit #include <unistd.h> next to <android/performance_hint.h> so gettid() no longer rides on transitive Oboe/NDK includes.
• Throttle updateLatency() to every 256 callbacks while leaving LatencyTuner::tune() at 128 — halves AAudio syscall pressure on the audio thread.
• Fix TOCTOU in nOboeGetLastErrorMessage: previous code returned lastError_.c_str() after releasing the mutex, so a concurrent Oboe error callback could mutate the std::string before the P/Invoke marshaller copied it. getLastError() now returns by value (copy under lock); the C export stages it into a thread_local snapshot whose lifetime covers the marshal step. Managed ABI unchanged.

// oboe_bridge.cpp — race-safe export
OSU_EXPORT const char* nOboeGetLastErrorMessage(intptr_t ptr) {
    auto* bridge = reinterpret_cast<OboeBridge*>(ptr);
    if (!bridge) return nullptr;
    thread_local std::string snapshot;
    snapshot = bridge->getLastError();   // copy under mutex, by value
    return snapshot.empty() ? nullptr : snapshot.c_str();
}

Not touched

vulkan_bridge.cpp (runs once at startup), the C# wrapper, and both submodule forks — none need changes for these wins.