Fix PowerManager race condition by raising events synchronously

[guimafelipe]

Description

Fixes the race condition in \SystemSuspendStatusChanged\ (issue #5224) using the existing API — no new events or event args types needed.

Root Cause

All PowerManager callbacks follow this pattern:

1. OS callback fires → sets cached value (e.g., \m_systemSuspendStatus)
2. Calls \RaiseEvent()\ which uses \co_await resume_background()\ to post to a thread pool
3. Race window: between step 1 and the handler running on the thread pool, another OS callback can overwrite the cached value

For \SystemSuspendStatusChanged, this reliably happens on wake from standby: \PBT_APMRESUMEAUTOMATIC\ and \PBT_APMRESUMESUSPEND\ fire on separate threads in rapid succession, causing both handlers to read \ManualResume\ instead of \AutoResume\ then \ManualResume.

Fix

Raise events synchronously from the OS callback thread instead of posting to the thread pool. This ensures the cached value is stable when the handler reads the property.

For \SystemSuspendStatusChanged\ specifically, a \std::mutex\ serializes the concurrent OS callbacks (\PBT_APMRESUMEAUTOMATIC\ and \PBT_APMRESUMESUSPEND\ fire on separate threads).

All other callbacks (\EnergySaver, \Battery, \Display, \PowerSource, \EffectivePowerMode, \UserPresence, etc.) receive the same synchronous dispatch fix since they have the same theoretical vulnerability.

Why not a new API?

PR #6202 proposed adding \SystemSuspendStatusChanged2\ with typed event args. That's unnecessary because the race is in the dispatch mechanism, not the API surface. By raising events synchronously (removing the \co_await resume_background()\ gap), the existing \SystemSuspendStatus\ property always returns the correct value when read from within the event handler.

Changes

• \PowerNotifications.h: All *_Callback\ methods now call event objects directly instead of via \RaiseEvent()\
• \PowerNotifications.h: Added \m_suspendCallbackMutex\ to serialize concurrent suspend/resume OS callbacks
• No IDL changes, no new API surface, no breaking changes

Testing

Existing tests verify registration/unregistration and property reads. Full validation requires system suspend/resume events (put computer to standby, wake by pressing power button, verify \AutoResume\ followed by \ManualResume).

Fixes #5224