Release the compiled module on close

close() now clears _module (initialized to None) inside the active
context together with the function references; lifecycle test asserts
it is retained on failed activation and cleared after close.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/CelerisLab/lbm/block_stepper.py

@@ -57,7 +57,7 @@ class PeriodicBlockStepper:
         self._status = "new"
         self._step_count = 0
         self._allocations = []
-        self._stream = self._copy = self._step = None
+        self._stream = self._module = self._copy = self._step = None
         with self.ctx.activate():
             try:
                 free, _ = cuda.mem_get_info()
@@ -179,7 +179,7 @@ class PeriodicBlockStepper:
                         self._stream.synchronize()
                 except Exception as exc:
                     error = exc
-                self._copy = self._step = None
+                self._copy = self._step = self._module = None
                 for pointer in self._allocations:
                     try:
                         pointer.free()