[dsmr] Add deprecated std::string overload for set_decryption_key (#14180)

esphome/components/dsmr/dsmr.h

@@ -64,6 +64,9 @@ class Dsmr : public Component, public uart::UARTDevice {
   void dump_config() override;
 
   void set_decryption_key(const char *decryption_key);
+  // Remove before 2026.8.0
+  ESPDEPRECATED("Pass .c_str() - e.g. set_decryption_key(key.c_str()). Removed in 2026.8.0", "2026.2.0")
+  void set_decryption_key(const std::string &decryption_key) { this->set_decryption_key(decryption_key.c_str()); }
   void set_max_telegram_length(size_t length) { this->max_telegram_len_ = length; }
   void set_request_pin(GPIOPin *request_pin) { this->request_pin_ = request_pin; }
   void set_request_interval(uint32_t interval) { this->request_interval_ = interval; }

tests/components/dsmr/common.yaml

@@ -1,4 +1,13 @@
+esphome:
+  on_boot:
+    then:
+      - lambda: |-
+          // Test deprecated std::string overload still compiles
+          std::string key = "00112233445566778899aabbccddeeff";
+          id(dsmr_instance).set_decryption_key(key);
+
 dsmr:
+  id: dsmr_instance
   decryption_key: 00112233445566778899aabbccddeeff
   max_telegram_length: 1000
   request_pin: ${request_pin}