misc: a few compiler level performance optimisations (#6559)

* window: use const references instead of copies

use const references instead of wasteful copies and make the = operator
check for self assignment and return early. also use const in all the
other operators.

* listener: pass std::function as const reference

instead of copies pass the std::functions as const references.

* config: dont unnecessarily convert to c_str

getHyprlangConfigValuePtr wants an std::string and we already have an
std::string, dont convert it to a c_str only for it to be converted back
to an std::string.

* buffer: pass attributes as const reference

pass attributes as const reference instead of copies.

src/config/ConfigValue.hpp

@@ -11,7 +11,7 @@ template <typename T>
 class CConfigValue {
   public:
     CConfigValue(const std::string& val) {
-        const auto PVHYPRLANG = g_pConfigManager->getHyprlangConfigValuePtr(val.c_str());
+        const auto PVHYPRLANG = g_pConfigManager->getHyprlangConfigValuePtr(val);
 
         p_ = PVHYPRLANG->getDataStaticPtr();