python3Packages.pycyphal: fix doctests on python 3.14 (#518654)

pkgs/development/python-modules/pycyphal/default.nix

@@ -2,6 +2,7 @@
   lib,
   buildPythonPackage,
   fetchFromGitHub,
+  pythonAtLeast,
 
   # build system
   setuptools,
@@ -34,6 +35,9 @@ buildPythonPackage rec {
     fetchSubmodules = true;
   };
 
+  # Set an event loop in the doctest helper; policy.get_event_loop no longer auto-creates one on 3.14.
+  patches = lib.optional (pythonAtLeast "3.14") ./python-3.14-asyncio-loop.patch;
+
   build-system = [ setuptools ];
 
   pythonRelaxDeps = [ "numpy" ];

pkgs/development/python-modules/pycyphal/python-3.14-asyncio-loop.patch

@@ -0,0 +1,10 @@
+--- a/tests/__init__.py
++++ b/tests/__init__.py
+@@ -37,6 +37,7 @@
+     This function shall be invoked per test, because the test suite undoes its effect before starting the next test.
+     """
+     _logger.info("asyncio_allow_event_loop_access_from_top_level()")
++    asyncio.set_event_loop(asyncio.new_event_loop())
+
+     def swap(mod: Any, name: str, new: Any) -> None:
+         restore = _PATCH_RESTORE_PREFIX + name