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/sway/language.cpp

@@ -124,7 +124,7 @@ auto Language::update() -> void {
   ALabel::update();
 }
 
-auto Language::set_current_layout(std::string current_layout) -> void {
+auto Language::set_current_layout(const std::string& current_layout) -> void {
   label_.get_style_context()->remove_class(layout_.short_name);
   layout_ = layouts_map_[current_layout];
   label_.get_style_context()->add_class(layout_.short_name);