chore: checkpoint before Python removal

vendor/crypto-bigint/src/limb/bit_xor.rs

@@ -0,0 +1,19 @@
+//! Limb bit xor operations.
+
+use super::Limb;
+use core::ops::BitXor;
+
+impl Limb {
+    /// Calculates `a ^ b`.
+    pub const fn bitxor(self, rhs: Self) -> Self {
+        Limb(self.0 ^ rhs.0)
+    }
+}
+
+impl BitXor for Limb {
+    type Output = Limb;
+
+    fn bitxor(self, rhs: Self) -> Self::Output {
+        self.bitxor(rhs)
+    }
+}