fix(bb): initialize element::infinity() (#4664)

Points at infinity are rare enough that we can initialize this to reduce
MSAN (C++ memory sanitizer) noise without performance loss. Caused
uninitialized memory errors in kzg test (which likely shouldn't be
creating points at infinity, anyway)

barretenberg/cpp/src/barretenberg/ecc/groups/element_impl.hpp

@@ -494,7 +494,7 @@ template <class Fq, class Fr, class T> constexpr element<Fq, Fr, T> element<Fq,
 
 template <class Fq, class Fr, class T> element<Fq, Fr, T> element<Fq, Fr, T>::infinity()
 {
-    element<Fq, Fr, T> e;
+    element<Fq, Fr, T> e{};
     e.self_set_infinity();
     return e;
 }