k256: point patch.crates-io at group fork for wNAF optimizations

Depends on https://github.com/RustCrypto/group/pull/XX (42Pupusas/group
wnaf-optimizations branch) which adds from_le_bytes, multiscalar_mul_array,
fixes wnaf_table sizing, and pre-sizes Vec allocations.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 42Pupusas

Cargo.lock

@@ -28,4 +28,4 @@ primefield = { path = "primefield" }
 primeorder = { path = "primeorder" }
 
 elliptic-curve = { git = "http://github.com/RustCrypto/traits.git" }
-rustcrypto-group = { path = "../group" }
+rustcrypto-group = { git = "https://github.com/42Pupusas/group.git", branch = "wnaf-optimizations" }