Fix various warnings and deprecations (#23641)

* Migrate to fastapi lifespan for startup events

The `on_event` style decorator is deprecated

https://fastapi.tiangolo.com/advanced/events/

* Migrate to pydantic TypeAdapter

https://pydantic.dev/docs/validation/2.12/get-started/migration/#introduction-of-typeadapter

* Replace pytz with native tz-aware objects and zoneinfo library

Supported from Python 3.9, see https://peps.python.org/pep-0615/. Also
https://blog.ganssle.io/articles/2019/11/utcnow.html.

Also provide tzdata as new dependency to supplement systems without local
tzdata information.

* Provide lookup for normalized timezone names

This provides a helper to look up the correct timezone name independent
of the casing of the given timezone name.

* Test timezone naming normalization and error handling

frigate/util/time.py

@@ -3,17 +3,32 @@
 import datetime
 import logging
 import math
-from zoneinfo import ZoneInfoNotFoundError
+from typing import Final
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError, available_timezones
 
-import pytz
 from tzlocal import get_localzone
 
 logger = logging.getLogger(__name__)
 
+TIMEZONE_CASEFOLD_INDEX: Final = {
+    timezone.casefold(): timezone for timezone in available_timezones()
+}
+
+
+def get_normalized_tz_name(tz_name: str) -> str:
+    """Return the canonical name for a case-insensitive IANA timezone."""
+    tz = TIMEZONE_CASEFOLD_INDEX.get(tz_name.casefold())
+    if tz:
+        return tz
+
+    raise ValueError(f"Unknown timezone: {tz_name}")
+
 
 def get_tz_modifiers(tz_name: str) -> tuple[str, str, float]:
     seconds_offset = (
-        datetime.datetime.now(pytz.timezone(tz_name)).utcoffset().total_seconds()
+        datetime.datetime.now(ZoneInfo(get_normalized_tz_name(tz_name)))
+        .utcoffset()
+        .total_seconds()
     )
     hours_offset = int(seconds_offset / 60 / 60)
     minutes_offset = int(seconds_offset / 60 - hours_offset * 60)
@@ -26,7 +41,7 @@ def get_tomorrow_at_time(hour: int) -> datetime.datetime:
     """Returns the datetime of the following day at 2am."""
     try:
         tomorrow = datetime.datetime.now(get_localzone()) + datetime.timedelta(days=1)
-    except ZoneInfoNotFoundError:
+    except (ValueError, ZoneInfoNotFoundError):
         tomorrow = datetime.datetime.now(datetime.UTC) + datetime.timedelta(days=1)
         logger.warning(
             "Using utc for maintenance due to missing or incorrect timezone set"
@@ -84,8 +99,8 @@ def get_dst_transitions(
         continuous periods with the same UTC offset
     """
     try:
-        tz = pytz.timezone(tz_name)
-    except pytz.UnknownTimeZoneError:
+        tz = ZoneInfo(get_normalized_tz_name(tz_name))
+    except (ValueError, ZoneInfoNotFoundError):
         # If timezone is invalid, return single period with no offset
         return [(start_time, end_time, 0)]