Add Windows specific shutdown code paths so stopping of child processes
is more reliable:
- stopping llama-swap won't leave behind any child processes it created
- uses Job Objects in Windows so the whole llama-swap tree is closed by
the os
- add procCtx to baseRouter. It replaces shutdownCtx as a signal for
managing lifetime state.
- shutdownCtx is only used by the router to stop handling new requests
during shutdown
- improve debug logging to make it easier to trace source of issues
Fixes#804
Updates #807
Benson Wong