tests(google-cloud-bigquery-storage): drop usage of pytz in tests/*.py (#15480)

This PR resolves the following failure which appears in 

```
==================================== ERRORS ====================================
________________ ERROR collecting tests/unit/test_reader_v1.py _________________
ImportError while importing test module '/tmpfs/src/github/google-cloud-python/packages/google-cloud-bigquery-storage/tests/unit/test_reader_v1.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/local/lib/python3.14/importlib/__init__.py:88: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
tests/unit/test_reader_v1.py:31: in 
    from .helpers import SCALAR_BLOCKS, SCALAR_COLUMN_NAMES, SCALAR_COLUMNS
tests/unit/helpers.py:20: in 
    import pytz
E   ModuleNotFoundError: No module named 'pytz'
_____________ ERROR collecting tests/unit/test_reader_v1_arrow.py ______________
ImportError while importing test module '/tmpfs/src/github/google-cloud-python/packages/google-cloud-bigquery-storage/tests/unit/test_reader_v1_arrow.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/local/lib/python3.14/importlib/__init__.py:88: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
tests/unit/test_reader_v1_arrow.py:33: in 
    from .helpers import SCALAR_BLOCKS, SCALAR_COLUMN_NAMES, SCALAR_COLUMNS
tests/unit/helpers.py:20: in 
    import pytz
E   ModuleNotFoundError: No module named 'pytz'
```

`pytz` was used in tests but not explicitly installed. This PR removes
usage of `pytz` in tests, although it is still needed transitively via
`pandas`

Author: parthea

.librarian/generator-input/client-post-processing/bigquery-storage-integration.yaml

@@ -461,6 +461,8 @@ replacements:
       google-api-core==1.34.1
       libcst==0.2.5
       fastavro==0.21.2
+      # pytz is required by pandas
+      pytz
       pandas==1.0.5
       pyarrow==0.15.0
       google-auth==2.14.1

.librarian/state.yaml

@@ -892,7 +892,7 @@ libraries:
     tag_format: '{id}-v{version}'
   - id: google-cloud-bigquery-storage
     version: 2.36.0
-    last_generated_commit: bd94e0b8c4975af0a66dc1f846c63c77dbc0064e
+    last_generated_commit: 6b36371f6f3099624547e9ce4c1db304161e6afe
     apis:
       - path: google/cloud/bigquery/storage/v1beta2
         service_config: bigquerystorage_v1beta2.yaml

packages/google-cloud-bigquery-storage/noxfile.py

@@ -55,7 +55,6 @@
 PACKAGE_NAME = "google-cloud-bigquery-storage"
 
 UNIT_TEST_STANDARD_DEPENDENCIES = [
-    "cachetools",
     "mock",
     "asyncmock",
     "pytest",
@@ -85,7 +84,6 @@
 SYSTEM_TEST_LOCAL_DEPENDENCIES: List[str] = []
 SYSTEM_TEST_DEPENDENCIES: List[str] = []
 SYSTEM_TEST_EXTRAS: List[str] = [
-    "cryptography",
     "fastavro",
     "pandas",
     "pyarrow",

packages/google-cloud-bigquery-storage/testing/constraints-3.7.txt

@@ -7,9 +7,13 @@
 google-api-core==1.34.1
 libcst==0.2.5
 fastavro==0.21.2
+# pytz is required by pandas
+pytz
 pandas==1.0.5
 pyarrow==0.15.0
 google-auth==2.14.1
+# cryptography is a direct dependency of google-auth
+cryptography==38.0.3
 # TODO(https://github.com/googleapis/gapic-generator-python/issues/2453)
 # Add the minimum supported version of grpcio to constraints files
 proto-plus==1.22.3

packages/google-cloud-bigquery-storage/tests/system/reader/test_reader.py

@@ -22,7 +22,6 @@
 import uuid
 
 import pytest
-import pytz
 
 from google.cloud import bigquery
 
@@ -451,7 +450,9 @@ def test_decoding_data_types(
         "bool_field": True,
         "geography_field": "POINT(-49.3028 69.0622)",
         "person_struct_field": {"name": "John", "age": 42},
-        "timestamp_field": dt.datetime(2019, 8, 9, 13, 38, 22, 17896, tzinfo=pytz.UTC),
+        "timestamp_field": dt.datetime(
+            2019, 8, 9, 13, 38, 22, 17896, tzinfo=dt.timezone.utc
+        ),
         "date_field": dt.date(1995, 3, 17),
         "time_field": dt.time(16, 24, 51),
         "string_array_field": ["foo", "bar", "baz"],

packages/google-cloud-bigquery-storage/tests/unit/helpers.py

@@ -17,8 +17,6 @@
 import datetime
 import decimal
 
-import pytz
-
 SCALAR_COLUMNS = [
     {"name": "int_col", "type": "int64"},
     {"name": "float_col", "type": "float64"},
@@ -42,7 +40,7 @@
             "bytes_col": b"ascii bytes",
             "date_col": datetime.date(1998, 9, 4),
             "time_col": datetime.time(12, 0),
-            "ts_col": datetime.datetime(2000, 1, 1, 5, 0, tzinfo=pytz.utc),
+            "ts_col": datetime.datetime(2000, 1, 1, 5, 0, tzinfo=datetime.timezone.utc),
         },
         {
             "int_col": 456,
@@ -53,7 +51,7 @@
             "bytes_col": b"\xbb\xee\xff",
             "date_col": datetime.date(1995, 3, 2),
             "time_col": datetime.time(13, 37),
-            "ts_col": datetime.datetime(1965, 4, 3, 2, 1, tzinfo=pytz.utc),
+            "ts_col": datetime.datetime(1965, 4, 3, 2, 1, tzinfo=datetime.timezone.utc),
         },
     ],
     [
@@ -66,7 +64,9 @@
             "bytes_col": b"\x54\x69\x6d",
             "date_col": datetime.date(1970, 1, 1),
             "time_col": datetime.time(16, 20),
-            "ts_col": datetime.datetime(1991, 8, 25, 20, 57, 8, tzinfo=pytz.utc),
+            "ts_col": datetime.datetime(
+                1991, 8, 25, 20, 57, 8, tzinfo=datetime.timezone.utc
+            ),
         }
     ],
 ]