Various string cleanups (#30435)

* Remove some unnecessary string concatenations

* Replace some simple str.formats with f-strings

* Replace some string concatenations with f-strings

homeassistant/components/smartthings/__init__.py

@@ -279,7 +279,7 @@ class DeviceBroker:
             capabilities = device.capabilities.copy()
             slots = {}
             for platform_name in SUPPORTED_PLATFORMS:
-                platform = importlib.import_module("." + platform_name, self.__module__)
+                platform = importlib.import_module(f".{platform_name}", self.__module__)
                 if not hasattr(platform, "get_capabilities"):
                     continue
                 assigned = platform.get_capabilities(capabilities)

homeassistant/components/smartthings/smartapp.py

@@ -109,7 +109,7 @@ def get_webhook_url(hass: HomeAssistantType) -> str:
 
 
 def _get_app_template(hass: HomeAssistantType):
-    endpoint = "at " + hass.config.api.base_url
+    endpoint = f"at {hass.config.api.base_url}"
     cloudhook_url = hass.data[DOMAIN][CONF_CLOUDHOOK_URL]
     if cloudhook_url is not None:
         endpoint = "via Nabu Casa"