feat: introduce maximum bit width constant, use it where appropriate, export it in python bindings

compiler/tests/python/test_fhe_dialect.py

@@ -1,9 +1,13 @@
 import pytest
 from mlir.ir import Context, RankedTensorType, Location
-from concrete.lang import register_dialects
+from concrete.lang import register_dialects, MAXIMUM_BIT_WIDTH
 from concrete.lang.dialects import fhe
 
 
+def test_constants():
+    assert MAXIMUM_BIT_WIDTH == 7
+
+
 @pytest.mark.parametrize("width", list(range(1, 8)))
 def test_eint(width):
     ctx = Context()