[statsd] Use direct appends and stack buffer instead of str_sprintf

Co-authored-by: Clyde Stubbs <2366188+clydebarrow@users.noreply.github.com>

esphome/components/lvgl/lv_validation.py

@@ -413,6 +413,7 @@ class TextValidator(LValidator):
                 str_args = [str(x) for x in value[CONF_ARGS]]
                 arg_expr = cg.RawExpression(",".join(str_args))
                 format_str = cpp_string_escape(format_str)
+                # str_sprintf justified: user-defined format, can't optimize without permanent RAM cost
                 sprintf_str = f"str_sprintf({format_str}, {arg_expr}).c_str()"
                 if nanval := value.get(CONF_IF_NAN):
                     nanval = cpp_string_escape(nanval)

esphome/components/lvgl/lvgl_esphome.cpp

@@ -65,7 +65,10 @@ std::string lv_event_code_name_for(uint8_t event_code) {
   if (event_code < sizeof(EVENT_NAMES) / sizeof(EVENT_NAMES[0])) {
     return EVENT_NAMES[event_code];
   }
-  return str_sprintf("%2d", event_code);
+  // max 4 bytes: "%u" with uint8_t (max 255, 3 digits) + null
+  char buf[4];
+  snprintf(buf, sizeof(buf), "%u", event_code);
+  return buf;
 }
 
 static void rounder_cb(lv_disp_drv_t *disp_drv, lv_area_t *area) {

esphome/components/statsd/statsd.cpp

@@ -114,14 +114,23 @@ void StatsdComponent::update() {
     // This implies you can't explicitly set a gauge to a negative number without first setting it to zero.
     if (val < 0) {
       if (this->prefix_) {
-        out.append(str_sprintf("%s.", this->prefix_));
+        out.append(this->prefix_);
+        out.append(".");
       }
-      out.append(str_sprintf("%s:0|g\n", s.name));
+      out.append(s.name);
+      out.append(":0|g\n");
     }
     if (this->prefix_) {
-      out.append(str_sprintf("%s.", this->prefix_));
+      out.append(this->prefix_);
+      out.append(".");
     }
-    out.append(str_sprintf("%s:%f|g\n", s.name, val));
+    out.append(s.name);
+    // Buffer for ":" + value + "|g\n".
+    // %g uses max 13 chars for value (sign + 6 significant digits + e+xxx)
+    // Total: 1 + 13 + 4 = 18 chars + null, use 24 for safety
+    char val_buf[24];
+    snprintf(val_buf, sizeof(val_buf), ":%g|g\n", val);
+    out.append(val_buf);
 
     if (out.length() > SEND_THRESHOLD) {
       this->send_(&out);