Restrict Cython version (#131)

Cython version 3.1 introduces a bug. To reproduce:

```
from pyroaring import BitMap
bm = BitMap(range(1000))
repr(bm)
```

Author: Ezibenroc

setup.py

@@ -88,7 +88,7 @@
     version=VERSION,
     description='Library for handling efficiently sorted integer sets.',
     long_description=long_description,
-    setup_requires=['cython>=3.0.2'],
+    setup_requires=['cython>=3.0.2,<3.1.0'],
     url='https://github.com/Ezibenroc/PyRoaringBitMap',
     author='Tom Cornebize',
     author_email='[email protected]',

tox.ini

@@ -13,7 +13,7 @@ setenv =
 deps =
 	hypothesis
     pytest
-	cython>=3.0.2
+	cython>=3.0.2,<3.1.0
 passenv =
 	HYPOTHESIS_PROFILE
 	ROARING_BITSIZE