fix(core): don't floor an explicit interval:0 to 1ms

std::max(1L, interval*1000) turned a user's explicit "interval": 0 into a
1ms periodic refresh, i.e. a ~1000x/s busy loop that starves the GTK main
loop and leaks memory (mpris RSS growth, missing tooltips, frozen updates).
An explicit 0 now stays the 'no periodic refresh' sentinel. Fixes #4987,
#4842; helps #4864, #4917, #4998, #5145.

src/ALabel.cpp

@@ -25,8 +25,14 @@ ALabel::ALabel(const Json::Value& config, const std::string& name, const std::st
                     ? std::chrono::milliseconds::max()
                     : std::chrono::milliseconds(
                           (config_["interval"].isNumeric()
-                               ? std::max(1L,  // Minimum 1ms due to millisecond precision
+                               ? (config_["interval"].asDouble() > 0
-                                          static_cast<long>(config_["interval"].asDouble() * 1000))
+                                      // Minimum 1ms due to millisecond precision
+                                      ? std::max(1L, static_cast<long>(
+                                                         config_["interval"].asDouble() * 1000))
+                                      // An explicit interval of 0 means "no periodic refresh"
+                                      // (event-driven only). Flooring it to 1ms busy-loops the
+                                      // main thread; keep it as the 0 sentinel (see custom.cpp).
+                                      : 0L)
                                : 1000 * (long)interval))),
       default_format_(format_) {
   label_.set_name(name);