core: reserve vector sizes as much as we can (#9118)

avoid reallocations as much as possible with a few edge cases where the
reservation overshoots a tiny bit. but a few bytes of memory short term
is better used then the overhead of potential reallocation.

src/desktop/Window.cpp

@@ -282,6 +282,8 @@ void CWindow::updateWindowDecos() {
 
     // make a copy because updateWindow can remove decos.
     std::vector<IHyprWindowDecoration*> decos;
+    // reserve to avoid reallocations
+    decos.reserve(m_dWindowDecorations.size());
 
     for (auto const& wd : m_dWindowDecorations) {
         decos.push_back(wd.get());