feat: add component-aware RFC 5424 application logging system

- Modify Rfc5424Formatter to read decnet_component from LogRecord
  and use it as RFC 5424 APP-NAME field (falls back to 'decnet')
- Add get_logger(component) factory in decnet/logging/__init__.py
  with _ComponentFilter that injects decnet_component on each record
- Wire all five layers to their component tag:
    cli -> 'cli', engine -> 'engine', api -> 'api' (api.py, ingester,
    routers), mutator -> 'mutator', collector -> 'collector'
- Add structured INFO/DEBUG/WARNING/ERROR log calls throughout each
  layer per the defined vocabulary; DEBUG calls are suppressed unless
  DECNET_DEVELOPER=true
- Add tests/test_logging.py covering factory, filter, formatter
  component-awareness, fallback behaviour, and level gating

decnet/config.py

@@ -48,8 +48,9 @@ class Rfc5424Formatter(logging.Formatter):
         msg      = record.getMessage()
         if record.exc_info:
             msg += "\n" + self.formatException(record.exc_info)
+        app = getattr(record, "decnet_component", self._app)
         return (
-            f"<{prival}>1 {ts} {self._hostname} {self._app}"
+            f"<{prival}>1 {ts} {self._hostname} {app}"
             f" {os.getpid()} {record.name} - {msg}"
         )