feat(auth): implement JWT TTL and expiration

added access_token_ttl setting
fixed public and private key mismatch while decoding jwt
decode_jwt now returns None on expired tokens instead of raising exc
generate_pair converts sub to string and uses dynamic expiration

core/exp.py

@@ -0,0 +1,7 @@
+from datetime import UTC, datetime, timedelta
+
+from config import cfg
+
+
+def get_exp(minutes: int = cfg.access_token_ttl) -> float:
+    return (datetime.now(UTC) + timedelta(minutes=minutes)).timestamp()