feat(espnow): add espnow-sender utility

Co-authored-by: Cursor <cursoragent@cursor.com>

espnow-sender/util.py

@@ -0,0 +1,12 @@
+def parse_mac(value):
+    raw = value.strip().lower().replace(":", "").replace("-", "")
+    if len(raw) != 12:
+        raise ValueError("address must be 12 hex chars or aa:bb:cc:dd:ee:ff")
+    try:
+        return bytes.fromhex(raw)
+    except ValueError:
+        raise ValueError("address contains non-hex characters")
+
+
+def format_mac(mac_bytes):
+    return ":".join("{:02x}".format(b) for b in mac_bytes)