Introduce a property to get the pointer to the underlying bitmap

This is useful for FFI.

Author: Filip62

pyroaring/__init__.pyi

@@ -32,6 +32,10 @@ class AbstractBitMap:
     def __init__(self, values: Iterable[int] | None = None, copy_on_write: bool = False, optimize: bool = True) -> None:
         ...
 
+    @property
+    def ptr(self) -> int:
+        ...
+
     @property
     def copy_on_write(self) -> bool:
         ...

pyroaring/abstract_bitmap.pxi

@@ -1,5 +1,5 @@
 cimport croaring
-from libc.stdint cimport uint32_t, uint64_t, int64_t
+from libc.stdint cimport uint32_t, uint64_t, uintptr_t, int64_t
 from libcpp cimport bool
 from libcpp.vector cimport vector
 from libc.stdlib cimport free, malloc
@@ -174,6 +174,13 @@ cdef class AbstractBitMap:
         (<AbstractBitMap>bm)._c_bitmap = ptr
         return bm
 
+    @property
+    def ptr(self):
+        """
+        The pointer to the underlying CRoaring bitmap as an integer.
+        """
+        return <uintptr_t>self._c_bitmap
+
     @property
     def copy_on_write(self):
         """