fix!: some sensors should be "unavailable" when the tracker is offline

[andreasbrett]

Following sensors IMHO should not retain their last value but rather show up as unavailable when the tracker itself is offline (either because it is turned off or because it has no reception):

• the device_tracker itself

binary sensors

• valid signal

sensors

• cell tower ID
• gsm strength
• GPS satellites
• battery

One could argue to let the battery retain its last state. IMHO it is better to indicate that the state is unclear. In the end the actual value could be far off from the last retained one. I'm not married to that idea though. The other sensors though definitely make no sense to expose when there's no signal.

[codecov[bot]]

Codecov Report

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

Project coverage is 98.12%. Comparing base (ac1cf1a) to head (3420a20). Report is 6 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #372 +/- ## ========================================== - Coverage 98.20% 98.12% -0.09% ========================================== Files 20 20 Lines 668 799 +131 ========================================== + Hits 656 784 +128 - Misses 12 15 +3 ``` | [Flag](https://app.codecov.io/gh/eifinger/hass-weenect/pull/372/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Kevin+Eifinger) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/eifinger/hass-weenect/pull/372/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Kevin+Eifinger) | `98.12% <100.00%> (-0.09%)` | :arrow_down: | 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=Kevin+Eifinger#carryforward-flags-in-the-pull-request-comment) to find out more.

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[eifinger]

Nice! Thank you!!