pytest_doctest_docutils(feat): Add _unblock_doctest helper for pytest 8.1+

why: Enable programmatic re-enabling of built-in doctest plugin using
the public unblock() API introduced in pytest 8.1.0.
what:
- Add PYTEST_VERSION constant for version-specific feature detection
- Add _unblock_doctest() helper that uses pluginmanager.unblock() when
  available, with graceful fallback for older pytest versions

Author: tony

src/pytest_doctest_docutils.py

@@ -37,6 +37,9 @@
 
 logger = logging.getLogger(__name__)
 
+# Parse pytest version for version-specific features
+PYTEST_VERSION = tuple(int(x) for x in pytest.__version__.split(".")[:2])
+
 # Lazy definition of runner class
 RUNNER_CLASS = None
 
@@ -68,6 +71,28 @@ def pytest_configure(config: pytest.Config) -> None:
         config.pluginmanager.set_blocked("doctest")
 
 
+def _unblock_doctest(config: pytest.Config) -> bool:
+    """Unblock doctest plugin (pytest 8.1+ only).
+
+    Re-enables the built-in doctest plugin after it was blocked by
+    pytest_configure. Uses the public unblock() API introduced in pytest 8.1.0.
+
+    Parameters
+    ----------
+    config : pytest.Config
+        The pytest configuration object
+
+    Returns
+    -------
+    bool
+        True if unblocked successfully, False if API not available
+    """
+    pm = config.pluginmanager
+    if PYTEST_VERSION >= (8, 1) and hasattr(pm, "unblock"):
+        return pm.unblock("doctest")
+    return False
+
+
 def pytest_unconfigure() -> None:
     """Unconfigure hook for pytest-doctest-docutils."""
     global RUNNER_CLASS