Replace pytz with standard library datetime timezones. (PP-3821) (#893)

## Description

- Replaces `pytz` with standard library datetime timezones.
- Removes `pytz` from project dependencies.

## Motivation and Context

`pytz` use is discouraged for Python 3.9 and later. Our minimum
supported version is 3.12. And nice to have one less dependency to deal
with.

[Jira PP-3821]

## How Has This Been Tested?

- No tests were changed.
- All tests continue to pass locally.
- CI tests.

## Checklist

- N/A - I have updated the documentation accordingly.
- [x] All new and existing tests passed.

Author: tdilauro

poetry.lock

@@ -40,7 +40,6 @@ Pillow = "*"
 pycryptodome = "*"
 PyJWT = "*"
 python = ">=3.12,<4"
-pytz = "^2026.1"
 requests = "2.32.5"
 SQLAlchemy = "^1.4"
 uszipcode = "==1.0.1"

pyproject.toml

@@ -1,11 +1,9 @@
 import datetime
 
-import pytz
-
 
 def utc_now() -> datetime.datetime:
     """Get the current time in UTC.
 
     :return: datetime object
     """
-    return datetime.datetime.now(tz=pytz.UTC)
+    return datetime.datetime.now(tz=datetime.UTC)

src/palace/registry/util/datetime_helpers.py

@@ -2,7 +2,6 @@
 import datetime
 import logging
 
-import pytz
 from jwt.algorithms import HMACAlgorithm
 
 from palace.registry.util.datetime_helpers import utc_now
@@ -43,12 +42,12 @@ def adobe_base64_decode(cls, to_decode):
         return base64.decodebytes(to_decode)
 
     JWT_EPOCH = datetime.datetime(
-        1970, 1, 1, tzinfo=pytz.UTC
+        1970, 1, 1, tzinfo=datetime.UTC
     )  # The JWT spec takes January 1 1970 as the epoch.
 
     # For the sake of shortening tokens, the Short Client Token spec takes January 1 2017 as the epoch,
     # and measures time in minutes rather than seconds.
-    SCT_EPOCH = datetime.datetime(2017, 1, 1, tzinfo=pytz.UTC)
+    SCT_EPOCH = datetime.datetime(2017, 1, 1, tzinfo=datetime.UTC)
 
     @classmethod
     def sct_numericdate(cls, d):