fix: disambiguate is_identity() calls between WeierstrassPoint and Group traits

Both traits define is_identity() with identical behavior (checks z == 0).
Qualify ambiguous call sites as Group::is_identity() to resolve.

Author: Tuanlinh12312

extensions/weierstrass_ec/guest/src/ecdsa.rs

@@ -94,7 +94,7 @@ where
     pub fn from_affine(point: AffinePoint<C>) -> Result<Self> {
         // Internally this calls `is_eq` on `x` and `y` coordinates, which will assert `x, y` are
         // reduced.
-        if point.is_identity() {
+        if Group::is_identity(&point) {
             Err(Error::new())
         } else {
             Ok(Self { point })
@@ -145,7 +145,7 @@ where
     }
 
     pub fn to_sec1_bytes(&self, compress: bool) -> Vec<u8> {
-        if self.point.is_identity() {
+        if Group::is_identity(&self.point) {
             return vec![0x00];
         }
 
@@ -533,7 +533,7 @@ where
     let R = <C as IntrinsicCurve>::msm(&[u1, u2], &[G, Q]);
     // For Coordinate<C>: IntMod, the internal implementation of is_identity will assert z
     // coordinate of R is reduced.
-    if R.is_identity() {
+    if Group::is_identity(&R) {
         return Err(Error::new());
     }
     let (x_1, _, _) = R.normalize().into_coords();

extensions/weierstrass_ec/guest/src/weierstrass.rs

@@ -124,7 +124,7 @@ where
         let table = bases
             .iter()
             .map(|base| {
-                if base.is_identity() {
+                if Group::is_identity(base) {
                     vec![<C::Point as Group>::IDENTITY; window_size - 2]
                 } else {
                     let mut multiples = Vec::with_capacity(window_size - 2);