added dedicated test file and moved timed_cache to tools

libp2p/tools/timed_cache/last_seen_cache.py

@@ -0,0 +1,22 @@
+import time
+
+from .base_timed_cache import (
+    BaseTimedCache,
+)
+
+
+class LastSeenCache(BaseTimedCache):
+    """Cache where expiry is updated on every access."""
+
+    def add(self, key: bytes) -> bool:
+        with self.lock:
+            is_new = key not in self.cache
+            self.cache[key] = int(time.time()) + self.ttl
+            return is_new
+
+    def has(self, key: bytes) -> bool:
+        with self.lock:
+            if key in self.cache:
+                self.cache[key] = int(time.time()) + self.ttl
+                return True
+            return False