Use PEP 526 type annotations, add some type hints (#26464)

* Add some more type hints to helpers.event

* Change most type comments to variable types

* Remove some superfluous type hints

homeassistant/components/startca/sensor.py

@@ -18,8 +18,8 @@ _LOGGER = logging.getLogger(__name__)
 DEFAULT_NAME = "Start.ca"
 CONF_TOTAL_BANDWIDTH = "total_bandwidth"
 
-GIGABYTES = "GB"  # type: str
-PERCENT = "%"  # type: str
+GIGABYTES = "GB"
+PERCENT = "%"
 
 MIN_TIME_BETWEEN_UPDATES = timedelta(hours=1)
 REQUEST_TIMEOUT = 5  # seconds