Properly escape backlashes in E614_REGEX (#47)

Using r-strings to avoid the new "invalid escape sequence" `SyntaxWarning` in Python 3.12

Author: Polsaker

lightspark/lightspark_client.py

@@ -1016,5 +1016,4 @@ def fail_htlcs(self, invoice_id: str, cancel_invoice: bool = True) -> str:
         return json["fail_htlcs"]["invoice"]["id"]
 
 
-# pylint: disable=anomalous-backslash-in-string
-E614_REGEX = re.compile("^\+?[1-9]\d{1,14}$")
+E614_REGEX = re.compile(r"^\+?[1-9]\d{1,14}$")