fix: avoid dereferencing past-the-end vector iterators in serialize.hpp

Two write() overloads in serialize.hpp used `&*buf.end()` to get a
pointer to the newly-appended region after resize(). Under
_GLIBCXX_DEBUG (enabled in asan-fast and debug presets since #22218),
dereferencing end() triggers a debug assertion abort.

Replace with `buf.data() + buf.size()` which achieves the same
pointer arithmetic without dereferencing any iterator.

Author: AztecBot

barretenberg/cpp/src/barretenberg/common/serialize.hpp

@@ -163,7 +163,7 @@ void read(std::vector<uint8_t> const& buf, std::integral auto& value)
 void write(std::vector<uint8_t>& buf, const std::integral auto& value)
 {
     buf.resize(buf.size() + sizeof(value));
-    uint8_t* ptr = &*buf.end() - sizeof(value);
+    uint8_t* ptr = buf.data() + buf.size() - sizeof(value);
     write(ptr, value);
 }
 
@@ -248,7 +248,7 @@ inline void write(std::ostream& os, std::vector<uint8_t> const& value)
 template <size_t N> inline void write(std::vector<uint8_t>& buf, std::array<uint8_t, N> const& value)
 {
     buf.resize(buf.size() + N);
-    auto* ptr = &*buf.end() - N;
+    auto* ptr = buf.data() + buf.size() - N;
     write(ptr, value);
 }