Huawei LTE sensor improvements (home-assistant#84019)

* Use `None` for unknown states consistently

* Use huawei_lte_api NetworkModeEnum instead of magic strings

* Recognize some new sensor items

* Exclude current day duration sensor

* Fix current month upload/download types

* Add current day transfer

* Extract lambdas used in multiple spots to named functions

* Formatter naming consistency improvements

Author: scop