Add postcode boundary calculation

pipeline/transform/postcode_boundaries/memory.py

@@ -0,0 +1,11 @@
+import ctypes
+import gc
+
+
+def release_memory() -> None:
+    """Force Python + glibc to release freed memory back to the OS."""
+    gc.collect()
+    try:
+        ctypes.CDLL("libc.so.6").malloc_trim(0)
+    except OSError:
+        pass