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>

include/modules/disk.hpp

@@ -22,7 +22,7 @@ class Disk : public ALabel {
   std::string path_;
   std::string unit_;
 
-  float calc_specific_divisor(const std::string divisor);
+  float calc_specific_divisor(const std::string& divisor);
 };
 
 }  // namespace waybar::modules