ref: speed up flagpole tests (#74949)

```console
$ time pytest tests/flagpole/
/Users/asottile/workspace/sentry/.venv/lib/python3.11/site-packages/phabricator/__init__.py:12: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
  __version__ = __import__('pkg_resources') \
============================== test session starts ==============================
platform darwin -- Python 3.11.8, pytest-8.0.0, pluggy-1.4.0
django: version: 5.0.7
rootdir: /Users/asottile/workspace/sentry
configfile: pyproject.toml
plugins: fail-slow-0.3.0, rerunfailures-11.0, json-report-1.5.0, metadata-3.1.1, time-machine-2.13.0, xdist-3.0.2, pytest_sentry-0.3.0, anyio-3.7.1, django-4.8.0, cov-4.0.0
collected 45 items                                                              

tests/flagpole/test_conditions.py ..........................              [ 57%]
tests/flagpole/test_evaluation_context.py .........                       [ 77%]
tests/flagpole/test_feature.py ..........                                 [100%]

============================== 45 passed in 4.22s ===============================

real	0m7.365s
user	0m4.001s
sys	0m0.634s
$ git apply patch
$ time pytest tests/flagpole/
/Users/asottile/workspace/sentry/.venv/lib/python3.11/site-packages/phabricator/__init__.py:12: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
  __version__ = __import__('pkg_resources') \
============================== test session starts ==============================
platform darwin -- Python 3.11.8, pytest-8.0.0, pluggy-1.4.0
django: version: 5.0.7
rootdir: /Users/asottile/workspace/sentry
configfile: pyproject.toml
plugins: fail-slow-0.3.0, rerunfailures-11.0, json-report-1.5.0, metadata-3.1.1, time-machine-2.13.0, xdist-3.0.2, pytest_sentry-0.3.0, anyio-3.7.1, django-4.8.0, cov-4.0.0
collected 45 items                                                              

tests/flagpole/test_conditions.py ..........................              [ 57%]
tests/flagpole/test_evaluation_context.py .........                       [ 77%]
tests/flagpole/test_feature.py ..........                                 [100%]

============================== 45 passed in 0.55s ===============================

real	0m3.489s
user	0m2.584s
sys	0m0.549s
```

<!-- Describe your PR here. -->

tests/flagpole/test_conditions.py

@@ -1,5 +1,6 @@
 from typing import Any
 
+import orjson
 import pytest
 from pydantic import ValidationError
 
@@ -15,11 +16,9 @@
     NotInCondition,
     create_case_insensitive_set_from_list,
 )
-from sentry.testutils.cases import TestCase
-from sentry.utils import json
 
 
-class TestCreateCaseInsensitiveSetFromList(TestCase):
+class TestCreateCaseInsensitiveSetFromList:
     def test_empty_set(self):
         assert create_case_insensitive_set_from_list([]) == set()
 
@@ -36,7 +35,7 @@ def test_returns_lowercase_string_set(self):
 def assert_valid_types(condition: type[ConditionBase], expected_types: list[Any]):
     for value in expected_types:
         condition_dict = dict(property="test", value=value)
-        json_condition = json.dumps(condition_dict)
+        json_condition = orjson.dumps(condition_dict)
         try:
             parsed_condition = condition.parse_raw(json_condition)
         except ValidationError as exc:
@@ -49,7 +48,7 @@ def assert_valid_types(condition: type[ConditionBase], expected_types: list[Any]
 def assert_invalid_types(condition: type[ConditionBase], invalid_types: list[Any]):
     for value in invalid_types:
         json_dict = dict(value=value)
-        condition_json = json.dumps(json_dict)
+        condition_json = orjson.dumps(json_dict)
         try:
             condition.parse_raw(condition_json)
         except ValidationError:
@@ -60,7 +59,7 @@ def assert_invalid_types(condition: type[ConditionBase], invalid_types: list[Any
         )
 
 
-class TestInConditions(TestCase):
+class TestInConditions:
     def test_invalid_values(self):
         with pytest.raises(ValidationError):
             InCondition(property="foo", value="bar")
@@ -144,7 +143,7 @@ def test_missing_context_property(self):
         )
 
 
-class TestContainsConditions(TestCase):
+class TestContainsConditions:
     def test_does_contain(self):
         condition = ContainsCondition(property="foo", value="bar")
         assert condition.match(
@@ -216,7 +215,7 @@ def test_missing_context_property(self):
             )
 
 
-class TestEqualsConditions(TestCase):
+class TestEqualsConditions:
     def test_is_equal_string(self):
         value = "foo"
         condition = EqualsCondition(property="foo", value=value)