fix some cython 3 todos

Author: mroeschke

pandas/_libs/algos.pyx

@@ -1089,8 +1089,7 @@ cdef void rank_sorted_1d(
     float64_t[::1] out,
     int64_t[::1] grp_sizes,
     const intp_t[:] sort_indexer,
-    # TODO(cython3): make const (https://github.com/cython/cython/issues/3222)
-    numeric_object_t[:] masked_vals,
+    const numeric_object_t[:] masked_vals,
     const uint8_t[:] mask,
     bint check_mask,
     Py_ssize_t N,
@@ -1378,16 +1377,15 @@ ctypedef fused out_t:
 @cython.boundscheck(False)
 @cython.wraparound(False)
 def diff_2d(
-    ndarray[diff_t, ndim=2] arr,  # TODO(cython3) update to "const diff_t[:, :] arr"
+    const diff_t[:, :] arr,
     ndarray[out_t, ndim=2] out,
     Py_ssize_t periods,
     int axis,
     bint datetimelike=False,
 ):
     cdef:
         Py_ssize_t i, j, sx, sy, start, stop
-        bint f_contig = arr.flags.f_contiguous
-        # bint f_contig = arr.is_f_contig()  # TODO(cython3) once arr is memoryview
+        bint f_contig = arr.is_f_contig()
         diff_t left, right
 
     # Disable for unsupported dtype combinations,

pandas/_libs/groupby.pyx

@@ -1435,14 +1435,12 @@ cdef inline void _check_below_mincount(
                         out[i, j] = 0
 
 
-# TODO(cython3): GH#31710 use memorviews once cython 0.30 is released so we can
-#  use `const numeric_object_t[:, :] values`
 @cython.wraparound(False)
 @cython.boundscheck(False)
 def group_last(
     numeric_object_t[:, ::1] out,
     int64_t[::1] counts,
-    ndarray[numeric_object_t, ndim=2] values,
+    const numeric_object_t[:, :] values,
     const intp_t[::1] labels,
     const uint8_t[:, :] mask,
     uint8_t[:, ::1] result_mask=None,
@@ -1502,14 +1500,12 @@ def group_last(
     )
 
 
-# TODO(cython3): GH#31710 use memorviews once cython 0.30 is released so we can
-#  use `const numeric_object_t[:, :] values`
 @cython.wraparound(False)
 @cython.boundscheck(False)
 def group_nth(
     numeric_object_t[:, ::1] out,
     int64_t[::1] counts,
-    ndarray[numeric_object_t, ndim=2] values,
+    const numeric_object_t[:, :] values,
     const intp_t[::1] labels,
     const uint8_t[:, :] mask,
     uint8_t[:, ::1] result_mask=None,