refactor: remove unused timezone import from __init__.py

Remove unused timezone import that was added in 4a57f79 for rate-limit
header parsing but became obsolete when rate-limit helper functions were
removed in 59c4212 (and also removed in upstream b1832c9).

No functional changes - purely cleanup of unused import.

Author: ericnoam

src/specify_cli/__init__.py

@@ -53,7 +53,7 @@
 import readchar
 import ssl
 import truststore
-from datetime import datetime, timezone
+from datetime import datetime
 
 ssl_context = truststore.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
 client = httpx.Client(verify=ssl_context)