fix: keep editor loop ticking while unfocused on Windows (issue #147)

Unity 6.4 parks the editor tick loop when the editor window is in the
background, so EditorApplication.delayCall callbacks scheduled by the
WebSocket handler never run and every MCP request times out until the
editor regains focus.

The main thread still pumps OS messages in the background, so a native
Win32 SetTimer callback keeps firing on the main thread; from there we
call EditorApplication.QueuePlayerLoopUpdate() every 100ms, which
flushes delayCall, coroutines and the synchronization context.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>