Add explicit tzdata dependency

Also removes obsolete import guard since Python 3.9+ guarantees zoneinfo
exists.

Fixes #188

Author: mattsta

ib_async/util.py

@@ -24,10 +24,7 @@
 
 import eventkit as ev
 
-try:
-    from zoneinfo import ZoneInfo
-except ImportError:
-    from backports.zoneinfo import ZoneInfo  # type: ignore
+from zoneinfo import ZoneInfo
 
 
 globalErrorEvent = ev.Event()

pyproject.toml

@@ -26,6 +26,7 @@ python = ">=3.10"
 aeventkit = "^2.1.0"
 # aeventkit = { path = "../eventkit", develop = true }
 nest_asyncio = "*"
+tzdata = "^2025.2"
 
 [tool.poetry.urls]
 "Bug Tracker" = "https://github.com/ib-api-reloaded/ib_async/issues"