refactor(test): Split test helpers into focused modules (#578)

This refactors the test helper functionality into separate modules and removes
unused path constants:

Breaking changes:
- Split libtmux.test into focused modules:
  - libtmux.test.constants: Test-related constants (TEST_SESSION_PREFIX, etc.)
  - libtmux.test.environment: Environment variable mocking
  - libtmux.test.random: Random string generation utilities
  - libtmux.test.temporary: Temporary session/window management
- Import paths have changed, requiring updates in downstream code
- Removed unused path constants:
  - current_dir
  - example_dir
  - fixtures_dir

Other changes:
- Add random to allowed builtins in pyproject.toml
- Update imports in pytest_plugin.py
- Add migration guide and changelog entries

This improves:
- Code organization through single-responsibility modules
- Maintainability via smaller, focused files
- Dependency clarity through explicit imports
- Testing capabilities by isolating components
- Codebase cleanliness by removing unused constants

Author: tony

CHANGES

@@ -15,6 +15,41 @@ $ pip install --user --upgrade --pre libtmux
 
 - _Future release notes will be placed here_
 
+### Breaking Changes
+
+#### Test helpers: Refactor
+
+Test helper functionality has been split into focused modules (#XXX):
+
+- `libtmux.test` module split into:
+  - `libtmux.test.constants`: Test-related constants (`TEST_SESSION_PREFIX`, etc.)
+  - `libtmux.test.environment`: Environment variable mocking
+  - `libtmux.test.random`: Random string generation utilities
+  - `libtmux.test.temporary`: Temporary session/window management
+
+**Breaking**: Import paths have changed. Update imports:
+
+```python
+# Old (0.45.x and earlier)
+from libtmux.test import (
+    TEST_SESSION_PREFIX,
+    get_test_session_name,
+    get_test_window_name,
+    namer,
+    temp_session,
+    temp_window,
+    EnvironmentVarGuard,
+)
+```
+
+```python
+# New (0.46.0+)
+from libtmux.test.constants import TEST_SESSION_PREFIX
+from libtmux.test.environment import EnvironmentVarGuard
+from libtmux.test.random import get_test_session_name, get_test_window_name, namer
+from libtmux.test.temporary import temp_session, temp_window
+```
+
 ### Development
 
 - CI: Check for runtime dependencies (#574)

MIGRATION

@@ -25,6 +25,41 @@ _Detailed migration steps for the next version will be posted here._
 
 <!-- To the maintainers and contributors: please add migration details for the upcoming release here -->
 
+## libtmux 0.45.x (Yet to be released)
+
+### Test helpers: Module moves
+
+Test helper functionality has been split into focused modules (#XXX):
+
+- `libtmux.test` module split into:
+  - `libtmux.test.constants`: Test-related constants (`TEST_SESSION_PREFIX`, etc.)
+  - `libtmux.test.environment`: Environment variable mocking
+  - `libtmux.test.random`: Random string generation utilities
+  - `libtmux.test.temporary`: Temporary session/window management
+
+**Breaking**: Import paths have changed. Update imports:
+
+```python
+# Old (0.45.x and earlier)
+from libtmux.test import (
+    TEST_SESSION_PREFIX,
+    get_test_session_name,
+    get_test_window_name,
+    namer,
+    temp_session,
+    temp_window,
+    EnvironmentVarGuard,
+)
+```
+
+```python
+# New (0.46.0+)
+from libtmux.test.constants import TEST_SESSION_PREFIX
+from libtmux.test.environment import EnvironmentVarGuard
+from libtmux.test.random import get_test_session_name, get_test_window_name, namer
+from libtmux.test.temporary import temp_session, temp_window
+```
+
 ## 0.35.0: Commands require explicit targets (2024-03-17)
 
 ### Commands require explicit targets (#535)

pyproject.toml

@@ -197,6 +197,7 @@ required-imports = [
 [tool.ruff.lint.flake8-builtins]
 builtins-allowed-modules = [
   "dataclasses",
+  "random",
   "types",
 ]
 

src/libtmux/pytest_plugin.py

@@ -13,7 +13,8 @@
 
 from libtmux import exc
 from libtmux.server import Server
-from libtmux.test import TEST_SESSION_PREFIX, get_test_session_name, namer
+from libtmux.test.constants import TEST_SESSION_PREFIX
+from libtmux.test.random import get_test_session_name, namer
 
 if t.TYPE_CHECKING:
     import pathlib