Every backend stored a instance reference, which wasn't used in most locations
which is redundant given that the state already tracks the instance for us as
well.
Previously we checked PEC support continuously at 10hz. With this change PEC support (or lack of support) is determined first before we try to read from the battery. Once determined, we do not repeat the checks.
Also simplified logic to determine PEC support based on version (should have no functional effect)
Also renamed get_pec_support to check_pec_support
Also renamed _pec_confirm to _pec_confirmed
