LogManager: add a mutex to protect stdoutStream

[da-x]

This is because QTextStream is not thread safe, as witnessed by this ASAN catch:

|    #0 0x7ffff78fb648 in realloc.part.0 (/lib64/libasan.so.8+0xfb648) (BuildId: 62576d6cef8744b024a915995656ecd4afeb4351)
|    #1 0x7ffff44fa2c7 in QArrayData::reallocateUnaligned(QArrayData*, void*, long long, long long, QArrayData::AllocationOption) (/lib64/libQt6Core.so.6+0x2fa2c7) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #2 0x7ffff44d025c in QArrayDataPointer<char16_t>::reallocateAndGrow(QArrayData::GrowthPosition, long long, QArrayDataPointer<char16_t>*) (/lib64/libQt6Core.so.6+0x2d025c) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #3 0x7ffff44ca21e in QString::append(QLatin1String) (/lib64/libQt6Core.so.6+0x2ca21e) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #4 0x7ffff4484bec in QTextStream::operator<<(QLatin1String) (/lib64/libQt6Core.so.6+0x284bec) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #5 0x6dec0e in qs::log::LogMessage::formatMessage(QTextStream&, qs::log::LogMessage const&, bool, bool, QString const&) /home/dan/dev/gh/da-x/quickshell/src/core/logging.cpp:101
|    #6 0x6dfaa3 in qs::log::LogManager::messageHandler(QtMsgType, QMessageLogContext const&, QString const&) /home/dan/dev/gh/da-x/quickshell/src/core/logging.cpp:166
|    #7 0x7ffff4326319 in qt_message_print(QtMsgType, QMessageLogContext const&, QString const&) (/lib64/libQt6Core.so.6+0x126319) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #8 0x7ffff432c2dd in qt_message_output(QtMsgType, QMessageLogContext const&, QString const&) (/lib64/libQt6Core.so.6+0x12c2dd) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #9 0x7ffff433e384 in QDebug::~QDebug() (/lib64/libQt6Core.so.6+0x13e384) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #10 0x7ffff44dfd55 in QScopedScopeLevelCounter::QScopedScopeLevelCounter(QThreadData*) (/lib64/libQt6Core.so.6+0x2dfd55) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #11 0x7ffff43af631 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (/lib64/libQt6Core.so.6+0x1af631) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #12 0x7ffff43b344d in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) (/lib64/libQt6Core.so.6+0x1b344d) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #13 0x7ffff46e2b86 in postEventSourceDispatch(_GSource*, int (*)(void*), void*) (/lib64/libQt6Core.so.6+0x4e2b86) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #14 0x7ffff130cf80 in g_main_context_dispatch_unlocked.lto_priv.0 (/lib64/libglib-2.0.so.0+0x5bf80) (BuildId: 8eb8a9a2c6a8fd0b4f3a00d75e20274c6c52e805)
|    #15 0x7ffff136cc67 in g_main_context_iterate_unlocked.isra.0 (/lib64/libglib-2.0.so.0+0xbbc67) (BuildId: 8eb8a9a2c6a8fd0b4f3a00d75e20274c6c52e805)
|    #16 0x7ffff130e35f in g_main_context_iteration (/lib64/libglib-2.0.so.0+0x5d35f) (BuildId: 8eb8a9a2c6a8fd0b4f3a00d75e20274c6c52e805)
|    #17 0x7ffff46e22f2 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (/lib64/libQt6Core.so.6+0x4e22f2) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #18 0x7ffff43bdcc9 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (/lib64/libQt6Core.so.6+0x1bdcc9) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #19 0x7ffff44e0c54 in QThread::exec() (/lib64/libQt6Core.so.6+0x2e0c54) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #20 0x7ffff458725e in QThreadPrivate::start(void*) (/lib64/libQt6Core.so.6+0x38725e) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #21 0x7ffff785e259 in asan_thread_start(void*) (/lib64/libasan.so.8+0x5e259) (BuildId: 62576d6cef8744b024a915995656ecd4afeb4351)
|    #22 0x7ffff4cbbb67 in start_thread (/lib64/libc.so.6+0x94b67) (BuildId: 9488b7bc91c299f62d05325020fbee9cfaf229bc)
|    #23 0x7ffff4d2c6bb in __clone3 (/lib64/libc.so.6+0x1056bb) (BuildId: 9488b7bc91c299f62d05325020fbee9cfaf229bc)
|
|0x50c00008fe00 is located 0 bytes inside of 128-byte region [0x50c00008fe00,0x50c00008fe80)
|freed by thread T2 (QDBusConnection) here:
|    #0 0x7ffff78fb648 in realloc.part.0 (/lib64/libasan.so.8+0xfb648) (BuildId: 62576d6cef8744b024a915995656ecd4afeb4351)
|    #1 0x7ffff44fa2c7 in QArrayData::reallocateUnaligned(QArrayData*, void*, long long, long long, QArrayData::AllocationOption) (/lib64/libQt6Core.so.6+0x2fa2c7) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|
|previously allocated by thread T1 (QThread) here:
|    #0 0x7ffff78fb648 in realloc.part.0 (/lib64/libasan.so.8+0xfb648) (BuildId: 62576d6cef8744b024a915995656ecd4afeb4351)
|    #1 0x7ffff44fa2c7 in QArrayData::reallocateUnaligned(QArrayData*, void*, long long, long long, QArrayData::AllocationOption) (/lib64/libQt6Core.so.6+0x2fa2c7) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|
|Thread T1 (QThread) created by T0 here:
|    #0 0x7ffff78f40a3 in pthread_create (/lib64/libasan.so.8+0xf40a3) (BuildId: 62576d6cef8744b024a915995656ecd4afeb4351)
|    #1 0x7ffff45868e8 in QThread::start(QThread::Priority) (/lib64/libQt6Core.so.6+0x3868e8) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #2 0x6e1049 in qs::log::LogManager::init(bool, bool, bool, QtMsgType, QString const&, QString const&) /home/dan/dev/gh/da-x/quickshell/src/core/logging.cpp:261
|    #3 0x46a94f in qs::launch::runCommand(int, char**, QCoreApplication*) /home/dan/dev/gh/da-x/quickshell/src/launch/command.cpp:500
|    #4 0x445373 in qs::launch::main(int, char**) /home/dan/dev/gh/da-x/quickshell/src/launch/main.cpp:112
|    #5 0x4374b5 in main /home/dan/dev/gh/da-x/quickshell/src/main.cpp:3
|    #6 0x7ffff4c5130d in __libc_start_call_main (/lib64/libc.so.6+0x2a30d) (BuildId: 9488b7bc91c299f62d05325020fbee9cfaf229bc)
|
|Thread T2 (QDBusConnection) created by T0 here:
|    #0 0x7ffff78f40a3 in pthread_create (/lib64/libasan.so.8+0xf40a3) (BuildId: 62576d6cef8744b024a915995656ecd4afeb4351)
|    #1 0x7ffff45868e8 in QThread::start(QThread::Priority) (/lib64/libQt6Core.so.6+0x3868e8) (BuildId: c21ff2de250ed0aba68ae0250f9a0d1c455f9fd3)
|    #2 0x7ffff613a166 in QDBusConnectionManager::instance() (/lib64/libQt6DBus.so.6+0x3d166) (BuildId: 35a23e05853374dafc6df118df20e91852bc6344)
|
|SUMMARY: AddressSanitizer: double-free (/lib64/libasan.so.8+0xfb648) (BuildId: 62576d6cef8744b024a915995656ecd4afeb4351) in realloc.part.0
|==3529858==ABORTING
|[Thread 0x7fffd40f56c0 (LWP 3529873) exited]
|[Thread 0x7fffd53ff6c0 (LWP 3529872) exited]
|[Inferior 1 (process 3529858) exited with code 01]