Migrate conftest.py and fib_test.py to pyre-strict

Summary:
## Summary:
Migrate 2 Python files from pyre-unsafe/no-directive to pyre-strict:

- `fbcode/eden/mononoke/tests/mock_restricted_path/test_infra/python/pytest/conftest.py`: Added `# pyre-strict` directive and return type annotation (`-> int`) to `my_fixture()`.
- `fbcode/hermetic_infra/fdb_playground/python/fib_test.py`: Replaced `# pyre-unsafe` with `# pyre-strict`. All existing type annotations and pyre-fixme comments for native C++ module imports are preserved.

`arc pyre check-changed-targets` confirms zero type errors across both files.
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Reviewed By: aperez

Differential Revision: D102427925

fbshipit-source-id: e132ad92b96e62acd5e3142a4b9888310a08c2a6

Author: generatedunixname893464919433493

eden/mononoke/tests/mock_restricted_path/test_infra/python/pytest/conftest.py

@@ -1,8 +1,13 @@
-# (c) Meta Platforms, Inc. and affiliates. Confidential and proprietary.
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2.
+
+# pyre-strict
 
 import pytest
 
 
 @pytest.fixture(scope="module")
-def my_fixture():
+def my_fixture() -> int:
     return 123