Remove dead code and use the event constants consistently

- drop unused BAR import, _VALID_MODES, _is_optional(),
  OPTIONAL_IMPORTS and is_loopback()
- replace hand-written event name strings with EVENT_INSERTED,
  EVENT_REMOVED and EVENT_INVALID, so a typo cannot silently
  disable an event path
- drop the now-moot pytest/coverage entries from .gitignore

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/rdm_card_reader/bridge.py

@@ -56,7 +56,7 @@ from collections import deque
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 from typing import Any, Callable, Deque, Dict, List, Optional
 
-from .card import EVENT_INSERTED, EVENT_REMOVED, CardEvent
+from .card import EVENT_INVALID, EVENT_INSERTED, EVENT_REMOVED, CardEvent
 
 #: Reader modes. ``login`` publishes inserts only (a tap = an authentication
 #: attempt). ``monitor`` publishes inserts and removals both.
@@ -111,7 +111,7 @@ class EventHub:
         self._last_at: Optional[float] = None
         self._mode = mode if mode in VALID_MODES else MODE_LOGIN
         self._started_at = time.time()
-        self._counts = {EVENT_INSERTED: 0, EVENT_REMOVED: 0, "invalid_card": 0}
+        self._counts = {EVENT_INSERTED: 0, EVENT_REMOVED: 0, EVENT_INVALID: 0}
         self._port: Optional[str] = None
         self._tap_ttl = float(tap_ttl if tap_ttl else 0.0)
         self._claimed_ttl = float(claimed_ttl if claimed_ttl else 0.0)
@@ -541,8 +541,3 @@ def create_server(
     server.token = token or os.environ.get("RDM_BRIDGE_TOKEN") or None  # type: ignore[attr-defined]
     server.logger = logger  # type: ignore[attr-defined]
     return server
-
-
-def is_loopback(host: str) -> bool:
-    """True for hosts that are not reachable off-box."""
-    return host in ("127.0.0.1", "::1", "localhost")