fix: cython 3.2 compatibility

bin/coverage.sh

@@ -18,7 +18,7 @@ pip uninstall -y cython
 pip install --pre cython       # unpinned to pick up new releases in CI
 # pip install cython==3.1.0a1  # known working version for Python < 3.13
 
-meson setup build -Dcoverage=true
+meson setup build -Dcoverage=true -Dflint_version_check=false
 spin run -- coverage run $RC -m flint.test $@
 coverage report $RC -m --sort=cover
 coverage html $RC

src/flint/flint_base/flint_base.pyx

@@ -474,7 +474,7 @@ cdef class flint_mpoly_context(flint_elem):
             fmpz_mpoly_ctx(3, '<Ordering.lex: 'lex'>', ('y', 'z', 'b'))
         """
         nvars = self.nvars()
-        gen_idxs = set(self.variable_to_index(i) for i in gens)
+        gen_idxs = {self.variable_to_index(i) for i in gens}
 
         if len(gens) > nvars:
             raise ValueError(f"expected at most {nvars} unique generators, got {len(gens)}")

src/flint/types/_gr.pyx

@@ -602,7 +602,7 @@ cdef class gr_ctx(flint_ctx):
     ###
     # Square Roots
 
-    def is_square(self, x) -> bool | None:
+    def is_square(self, x):
         """
         Returns whether x is a perfect square in the context.
         """

src/flint/typing.py

@@ -10,12 +10,14 @@
     Iterator,
     Iterable,
     Any,
-    Self,
     Mapping,
     Sequence,
     overload,
 )
 
+if TYPE_CHECKING:
+    from typing import Self
+
 from .flint_base.flint_base import (
     flint_elem,
     flint_scalar,