Fix: Make `fuel_level` and `fuel_range` optional

[CM000n]

It looks as if no fuel_level and fuel_range will be reported for fully electric vehicles such as the bz4x. With this MR, the two fields in the ElectricStatusModel are therefore made Optional. Please also see: https://github.com/DurgNomis-drol/mytoyota/issues/277#issuecomment-1880126616

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (d7237a2) 72.47% compared to head (3e5a970) 72.47%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #278 +/- ## ======================================= Coverage 72.47% 72.47% ======================================= Files 28 28 Lines 1355 1355 ======================================= Hits 982 982 Misses 373 373 ``` | [Flag](https://app.codecov.io/gh/DurgNomis-drol/mytoyota/pull/278/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Simon+Hansen) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/DurgNomis-drol/mytoyota/pull/278/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Simon+Hansen) | `72.47% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Simon+Hansen#carryforward-flags-in-the-pull-request-comment) to find out more.

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