perf(memory): optimize C++ string operations to reduce heap fragmentation

- Replaced pass-by-value std::string parameters with const std::string&
or std::string_view to prevent SSO overallocations.

- Refactored static mapping functions in UPower to return
std::string_view instead of constructing std::string literals, enabling
perfect cache locality.

- Optimized string concatenation in hot loops (network IPs, inhibitor
lists, sway window marks) by using std::string::append() and
pre-reserving capacity instead of overloaded operator+ which produces
temporary heap instances.

These optimizations reduce high-frequency memory churn and overall heap
fragmentation within the main rendering loops.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

src/modules/sni/host.cpp

@@ -132,7 +132,7 @@ std::tuple<std::string, std::string> Host::getBusNameAndObjectPath(const std::st
   return {service, "/StatusNotifierItem"};
 }
 
-void Host::addRegisteredItem(std::string service) {
+void Host::addRegisteredItem(const std::string& service) {
   std::string bus_name, object_path;
   std::tie(bus_name, object_path) = getBusNameAndObjectPath(service);
   auto it = std::find_if(items_.begin(), items_.end(), [&bus_name, &object_path](const auto& item) {