fix: Add missing ByteUtilities.h include and use coroStackSize constant

- Include ByteUtilities.h in Coro.ipp so megabytes() is declared
- Use coroStackSize constant in coroutine constructor instead of
  hardcoded 1536*1024, enabling sanitizer-aware stack sizing
- Initialize local variable in PropertyStream destructor to satisfy
  clang-tidy cppcoreguidelines-init-variables

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/libxrpl/beast/utility/beast_PropertyStream.cpp

@@ -161,7 +161,7 @@ PropertyStream::Source::~Source()
     // Read parent_ under lock, then release before calling remove()
     // to maintain consistent lock ordering (parent before child),
     // matching the order used in find_one_deep().
-    Source* parent;
+    Source* parent = nullptr;
     {
         std::lock_guard _(lock_);
         parent = parent_;