CLN: point cython3 TODOs at upstream cython#2485 (#65387)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jbrockmendel

pandas/_libs/hashtable_func_helper.pxi.in

@@ -450,7 +450,7 @@ cpdef ismember(ndarray[htfunc_t] arr, ndarray[htfunc_t] values):
 @cython.wraparound(False)
 @cython.boundscheck(False)
 def mode(ndarray[htfunc_t] values, bint dropna, const uint8_t[:] mask=None):
-    # TODO(cython3): use const htfunct_t[:]
+    # TODO(cython#2485): once possible, use const htfunc_t[:]
 
     cdef:
         ndarray[htfunc_t] keys

pandas/_libs/tslibs/period.pyx

@@ -1617,7 +1617,7 @@ cdef int64_t _extract_ordinal(object item, PeriodDtypeBase dtype) except? -1:
 @cython.wraparound(False)
 @cython.boundscheck(False)
 def extract_period_unit(ndarray[object] values) -> PeriodDtypeBase:
-    # TODO: Change type to const object[:] when Cython supports that.
+    # TODO(cython#2485): once possible, use const object[:]
 
     cdef:
         Py_ssize_t i, n = len(values)