feat(net): add {linkSpeed} format replacement

Adds an ethernet link speed ({linkSpeed}) read from
/sys/class/net/<iface>/speed, plus a skip-decimal option on pow_format
to drop a trailing .0. Rebased onto master's store-based network
formatting; existing compact bandwidth args updated for the new
pow_format signature.

include/modules/network.hpp

@@ -54,6 +54,7 @@ class Network : public ALabel {
   const std::string getNetworkState() const;
   void clearIface();
   std::optional<std::pair<unsigned long long, unsigned long long>> readBandwidthUsage();
+  uint32_t readLinkSpeed() const;
 
   int ifid_{-1};
   ip_addr_pref addr_pref_{ip_addr_pref::IPV4};
@@ -94,6 +95,7 @@ class Network : public ALabel {
   uint8_t signal_strength_;
   std::string signal_strength_app_;
   uint32_t route_priority;
+  uint32_t link_speed_{0};
 
   util::SleeperThread thread_;
   util::SleeperThread thread_timer_;